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Arduino Software (IDE)

The Arduino Integrated Development Environment - or Arduino Software (IDE) - contains a text editor for writing code, a message area, a text console, a toolbar with buttons for common functions and a series of menus. It connects to the Arduino and Genuino hardware to upload programs and communicate with them.

Writing Sketches

Programs written using Arduino Software (IDE) are called sketches. These sketches are written in the text editor and are saved with the file extension .ino. The editor has features for cutting/pasting and for searching/replacing text. The message area gives feedback while saving and exporting and also displays errors. The console displays text output by the Arduino Software (IDE), including complete error messages and other information. The bottom righthand corner of the window displays the configured board and serial port. The toolbar buttons allow you to verify and upload programs, create, open, and save sketches, and open the serial monitor.

NB: Versions of the Arduino Software (IDE) prior to 1.0 saved sketches with the extension .pde. It is possible to open these files with version 1.0, you will be prompted to save the sketch with the .ino extension on save.

	Verify Checks your code for errors compiling it.
	Upload Compiles your code and uploads it to the configured board. See uploading below for details. Note: If you are using an external programmer with your board, you can hold down the "shift" key on your computer when using this icon. The text will change to "Upload using Programmer"
	New Creates a new sketch.
	Open Presents a menu of all the sketches in your sketchbook. Clicking one will open it within the current window overwriting its content. Note: due to a bug in Java, this menu doesn't scroll; if you need to open a sketch late in the list, use the File | Sketchbook menu instead.
	Save Saves your sketch.
	Serial Monitor Opens the serial monitor.

Additional commands are found within the five menus: File, Edit, Sketch, Tools, Help. The menus are context sensitive, which means only those items relevant to the work currently being carried out are available.

File

• New
  Creates a new instance of the editor, with the bare minimum structure of a sketch already in place.
• Open
  Allows to load a sketch file browsing through the computer drives and folders.
• Open Recent
  Provides a short list of the most recent sketches, ready to be opened.
• Sketchbook
  Shows the current sketches within the sketchbook folder structure; clicking on any name opens the corresponding sketch in a new editor instance.
• Examples
  Any example provided by the Arduino Software (IDE) or library shows up in this menu item. All the examples are structured in a tree that allows easy access by topic or library.
• Close
  Closes the instance of the Arduino Software from which it is clicked.
• Save
  Saves the sketch with the current name. If the file hasn't been named before, a name will be provided in a "Save as.." window.
• Save as...
  Allows to save the current sketch with a different name.
• Page Setup
  It shows the Page Setup window for printing.
• Print
  Sends the current sketch to the printer according to the settings defined in Page Setup.
• Preferences
  Opens the Preferences window where some settings of the IDE may be customized, as the language of the IDE interface.
• Quit
  Closes all IDE windows. The same sketches open when Quit was chosen will be automatically reopened the next time you start the IDE.

Edit

• Undo/Redo
  Goes back of one or more steps you did while editing; when you go back, you may go forward with Redo.
• Cut
  Removes the selected text from the editor and places it into the clipboard.
• Copy
  Duplicates the selected text in the editor and places it into the clipboard.
• Copy for Forum
  Copies the code of your sketch to the clipboard in a form suitable for posting to the forum, complete with syntax coloring.
• Copy as HTML
  Copies the code of your sketch to the clipboard as HTML, suitable for embedding in web pages.
• Paste
  Puts the contents of the clipboard at the cursor position, in the editor.
• Select All
  Selects and highlights the whole content of the editor.
• Comment/Uncomment
  Puts or removes the // comment marker at the beginning of each selected line.
• Increase/Decrease Indent
  Adds or subtracts a space at the beginning of each selected line, moving the text one space on the right or eliminating a space at the beginning.
• Find
  Opens the Find and Replace window where you can specify text to search inside the current sketch according to several options.
• Find Next
  Highlights the next occurrence - if any - of the string specified as the search item in the Find window, relative to the cursor position.
• Find Previous
  Highlights the previous occurrence - if any - of the string specified as the search item in the Find window relative to the cursor position.

Sketch

• Verify/Compile
  Checks your sketch for errors compiling it; it will report memory usage for code and variables in the console area.
• Upload
  Compiles and loads the binary file onto the configured board through the configured Port.
• Upload Using Programmer
  This will overwrite the bootloader on the board; you will need to use Tools > Burn Bootloader to restore it and be able to Upload to USB serial port again. However, it allows you to use the full capacity of the Flash memory for your sketch. Please note that this command will NOT burn the fuses. To do so a Tools -> Burn Bootloader command must be executed.
• Export Compiled Binary
  Saves a .hex file that may be kept as archive or sent to the board using other tools.
• Show Sketch Folder
  Opens the current sketch folder.
• Include Library
  Adds a library to your sketch by inserting #include statements at the start of your code. For more details, see libraries below. Additionally, from this menu item you can access the Library Manager and import new libraries from .zip files.
• Add File...
  Adds a source file to the sketch (it will be copied from its current location). The new file appears in a new tab in the sketch window. Files can be removed from the sketch using the tab menu accessible clicking on the small triangle icon below the serial monitor one on the right side o the toolbar.

Tools

• Auto Format
  This formats your code nicely: i.e. indents it so that opening and closing curly braces line up, and that the statements inside curly braces are indented more.
• Archive Sketch
  Archives a copy of the current sketch in .zip format. The archive is placed in the same directory as the sketch.
• Fix Encoding & Reload
  Fixes possible discrepancies between the editor char map encoding and other operating systems char maps.
• Serial Monitor
  Opens the serial monitor window and initiates the exchange of data with any connected board on the currently selected Port. This usually resets the board, if the board supports Reset over serial port opening.
• Board
  Select the board that you're using. See below for descriptions of the various boards.
• Port
  This menu contains all the serial devices (real or virtual) on your machine. It should automatically refresh every time you open the top-level tools menu.
• Programmer
  For selecting a harware programmer when programming a board or chip and not using the onboard USB-serial connection. Normally you won't need this, but if you're burning a bootloader to a new microcontroller, you will use this.
• Burn Bootloader
  The items in this menu allow you to burn a bootloader onto the microcontroller on an Arduino board. This is not required for normal use of an Arduino or Genuino board but is useful if you purchase a new ATmega microcontroller (which normally come without a bootloader). Ensure that you've selected the correct board from the Boards menu before burning the bootloader on the target board. This command also set the right fuses.

Help

Here you find easy access to a number of documents that come with the Arduino Software (IDE). You have access to Getting Started, Reference, this guide to the IDE and other documents locally, without an internet connection. The documents are a local copy of the online ones and may link back to our online website.

• Find in Reference
  This is the only interactive function of the Help menu: it directly selects the relevant page in the local copy of the Reference for the function or command under the cursor.

Sketchbook

The Arduino Software (IDE) uses the concept of a sketchbook: a standard place to store your programs (or sketches). The sketches in your sketchbook can be opened from the File > Sketchbook menu or from the Open button on the toolbar. The first time you run the Arduino software, it will automatically create a directory for your sketchbook. You can view or change the location of the sketchbook location from with the Preferences dialog.

Beginning with version 1.0, files are saved with a .ino file extension. Previous versions use the .pde extension. You may still open .pde named files in version 1.0 and later, the software will automatically rename the extension to .ino.

Tabs, Multiple Files, and Compilation

Allows you to manage sketches with more than one file (each of which appears in its own tab). These can be normal Arduino code files (no visible extension), C files (.c extension), C++ files (.cpp), or header files (.h).

Uploading

Before uploading your sketch, you need to select the correct items from the Tools > Board and Tools > Port menus. The boards are described below. On the Mac, the serial port is probably something like /dev/tty.usbmodem241 (for an Uno or Mega2560 or Leonardo) or /dev/tty.usbserial-1B1 (for a Duemilanove or earlier USB board), or /dev/tty.USA19QW1b1P1.1 (for a serial board connected with a Keyspan USB-to-Serial adapter). On Windows, it's probably COM1 or COM2 (for a serial board) or COM4, COM5, COM7, or higher (for a USB board) - to find out, you look for USB serial device in the ports section of the Windows Device Manager. On Linux, it should be /dev/ttyACMx , /dev/ttyUSBx or similar. Once you've selected the correct serial port and board, press the upload button in the toolbar or select the Upload item from the Sketch menu. Current Arduino boards will reset automatically and begin the upload. With older boards (pre-Diecimila) that lack auto-reset, you'll need to press the reset button on the board just before starting the upload. On most boards, you'll see the RX and TX LEDs blink as the sketch is uploaded. The Arduino Software (IDE) will display a message when the upload is complete, or show an error.

When you upload a sketch, you're using the Arduino bootloader, a small program that has been loaded on to the microcontroller on your board. It allows you to upload code without using any additional hardware. The bootloader is active for a few seconds when the board resets; then it starts whichever sketch was most recently uploaded to the microcontroller. The bootloader will blink the on-board (pin 13) LED when it starts (i.e. when the board resets).

Libraries

Libraries provide extra functionality for use in sketches, e.g. working with hardware or manipulating data. To use a library in a sketch, select it from the Sketch > Import Library menu. This will insert one or more #include statements at the top of the sketch and compile the library with your sketch. Because libraries are uploaded to the board with your sketch, they increase the amount of space it takes up. If a sketch no longer needs a library, simply delete its #include statements from the top of your code.

There is a list of libraries in the reference. Some libraries are included with the Arduino software. Others can be downloaded from a variety of sources or through the Library Manager. Starting with version 1.0.5 of the IDE, you do can import a library from a zip file and use it in an open sketch. See these instructions for installing a third-party library.

To write your own library, see this tutorial.

Third-Party Hardware

Support for third-party hardware can be added to the hardware directory of your sketchbook directory. Platforms installed there may include board definitions (which appear in the board menu), core libraries, bootloaders, and programmer definitions. To install, create the hardware directory, then unzip the third-party platform into its own sub-directory. (Don't use "arduino" as the sub-directory name or you'll override the built-in Arduino platform.) To uninstall, simply delete its directory.

For details on creating packages for third-party hardware, see the Arduino IDE 1.5 3rd party Hardware specification.

Serial Monitor

This displays serial sent from the Arduino or Genuino board over USB or serial connector. To send data to the board, enter text and click on the "send" button or press enter. Choose the baud rate from the drop-down menu that matches the rate passed to Serial.begin in your sketch. Note that on Windows, Mac or Linux the board will reset (it will rerun your sketch) when you connect with the serial monitor. Please note that the Serial Monitor does not process control characters; if your sketch needs a complete management of the serial communication with control characters, you can use an external terminal program and connect it to the COM port assigned to your Arduino board.

You can also talk to the board from Processing, Flash, MaxMSP, etc (see the interfacing page for details).

Preferences

Some preferences can be set in the preferences dialog (found under the Arduino menu on the Mac, or File on Windows and Linux). The rest can be found in the preferences file, whose location is shown in the preference dialog.

Language Support

Since version 1.0.1 , the Arduino Software (IDE) has been translated into 30+ different languages. By default, the IDE loads in the language selected by your operating system. (Note: on Windows and possibly Linux, this is determined by the locale setting which controls currency and date formats, not by the language the operating system is displayed in.)

If you would like to change the language manually, start the Arduino Software (IDE) and open the Preferences window. Next to the Editor Language there is a dropdown menu of currently supported languages. Select your preferred language from the menu, and restart the software to use the selected language. If your operating system language is not supported, the Arduino Software (IDE) will default to English.

You can return the software to its default setting of selecting its language based on your operating system by selecting System Default from the Editor Language drop-down. This setting will take effect when you restart the Arduino Software (IDE). Similarly, after changing your operating system's settings, you must restart the Arduino Software (IDE) to update it to the new default language.

Boards

The board selection has two effects: it sets the parameters (e.g. CPU speed and baud rate) used when compiling and uploading sketches; and sets and the file and fuse settings used by the burn bootloader command. Some of the board definitions differ only in the latter, so even if you've been uploading successfully with a particular selection you'll want to check it before burning the bootloader. You can find a comparison table between the various boards here.

Arduino Software (IDE) includes the built in support for the boards in the following list, all based on the AVR Core. The Boards Manager included in the standard installation allows to add support for the growing number of new boards based on different cores like Arduino Due, Arduino Zero, Edison, Galileo and so on.

• Arduino Yùn
  An ATmega32u4 running at 16 MHz with auto-reset, 12 Analog In, 20 Digital I/O and 7 PWM.
• Arduino/Genuino Uno
  An ATmega328P running at 16 MHz with auto-reset, 6 Analog In, 14 Digital I/O and 6 PWM.
• Arduino Diecimila or Duemilanove w/ ATmega168
  An ATmega168 running at 16 MHz with auto-reset.
• Arduino Nano w/ ATmega328P
  An ATmega328P running at 16 MHz with auto-reset. Has eight analog inputs.
• Arduino/Genuino Mega 2560
  An ATmega2560 running at 16 MHz with auto-reset, 16 Analog In, 54 Digital I/O and 15 PWM.
• Arduino Mega
  An ATmega1280 running at 16 MHz with auto-reset, 16 Analog In, 54 Digital I/O and 15 PWM.
• Arduino Mega ADK
  An ATmega2560 running at 16 MHz with auto-reset, 16 Analog In, 54 Digital I/O and 15 PWM.
• Arduino Leonardo
  An ATmega32u4 running at 16 MHz with auto-reset, 12 Analog In, 20 Digital I/O and 7 PWM.
• Arduino/Genuino Micro
  An ATmega32u4 running at 16 MHz with auto-reset, 12 Analog In, 20 Digital I/O and 7 PWM.
• Arduino Esplora
  An ATmega32u4 running at 16 MHz with auto-reset.
• Arduino Mini w/ ATmega328P
  An ATmega328P running at 16 MHz with auto-reset, 8 Analog In, 14 Digital I/O and 6 PWM.
• Arduino Ethernet
  Equivalent to Arduino UNO with an Ethernet shield: An ATmega328P running at 16 MHz with auto-reset, 6 Analog In, 14 Digital I/O and 6 PWM.
• Arduino Fio
  An ATmega328P running at 8 MHz with auto-reset. Equivalent to Arduino Pro or Pro Mini (3.3V, 8 MHz) w/ ATmega328P, 6 Analog In, 14 Digital I/O and 6 PWM.
• Arduino BT w/ ATmega328P
  ATmega328P running at 16 MHz. The bootloader burned (4 KB) includes codes to initialize the on-board bluetooth module, 6 Analog In, 14 Digital I/O and 6 PWM..
• LilyPad Arduino USB
  An ATmega32u4 running at 8 MHz with auto-reset, 4 Analog In, 9 Digital I/O and 4 PWM.
• LilyPad Arduino
  An ATmega168 or ATmega132 running at 8 MHz with auto-reset, 6 Analog In, 14 Digital I/O and 6 PWM.
• Arduino Pro or Pro Mini (5V, 16 MHz) w/ ATmega328P
  An ATmega328P running at 16 MHz with auto-reset. Equivalent to Arduino Duemilanove or Nano w/ ATmega328P; 6 Analog In, 14 Digital I/O and 6 PWM.
• Arduino NG or older w/ ATmega168
  An ATmega168 running at 16 MHzwithout auto-reset. Compilation and upload is equivalent to Arduino Diecimila or Duemilanove w/ ATmega168, but the bootloader burned has a slower timeout (and blinks the pin 13 LED three times on reset); 6 Analog In, 14 Digital I/O and 6 PWM.
• Arduino Robot Control
  An ATmega328P running at 16 MHz with auto-reset.
• Arduino Robot Motor
  An ATmega328P running at 16 MHz with auto-reset.
• Arduino Gemma
  An ATtiny85 running at 8 MHz with auto-reset, 1 Analog In, 3 Digital I/O and 2 PWM.

For instructions on installing support for other boards, see third-party hardware above.

Last revision 2015/09/07 by SM

The text of the Arduino getting started guide is licensed under a Creative Commons Attribution-ShareAlike 3.0 License. Code samples in the guide are released into the public domain.

From the small business owner to the student creating a class project, or even casual individuals working on a blog or personal project online, HTML knowledge is incredibly useful. Although the prospect of having to learn a programming language certainly does seem daunting, the good news is that HTML uses common words so that it is fairly simple to pick up.

In this guide we cover the basics in a (hopefully) easy-to-understand manner, perfect for the absolute beginner. However, we don’t stop at the basics — even seasoned webmasters will find useful tips to expand your working knowledge of HTML. We will even dive into XHTML, DHTML, and the newest stuff in HTML5.

A Brief History of HTML 1-4

HTML was invented by Tim Berners-Lee in the late 1980s and early 1990s. The first “public” release was in 1991. It was based on an earlier markup language, SGML (Standardized General Markup Language).

The major innovation of HTML was its use of the hyperlink. We are so used to this now that it is hard to understand how revolutionary this idea was at the time.

The hyperlink allows any document to reference any other document, and provides immediate access to that other document. Hyperlinks are what make the World Wide Web a web, and not just a library or database.

The IETF took up HTML as a standard and published the first HTML proposal in 1993. HTML 2.0, the first full official specification was released in 1995. By 1997, the W3C had taken over stewardship of the standard, and HTML 3.2 was released.

HTML 4.0 was released towards the end of 1997, and again the following year with a few updates. This version of the standard, with its three variations (strict, transitional, and frameset) defined HTML most of the next decade.

It was the version in force during the rise of the web’s most iconic properties: Wikipedia, Google, Facebook, WordPress, Myspace, AOL. If you learned how to build web pages before 2008, you almost certainly learned this version.

Alongside HTML 4.0 was a related project called XHTML. This was first released in 2000 and 2001, as an XML-based implementation of HTML 4.0. Since XML had a stricter syntax than HTML, and could be easily validated by an XML parser, it was thought that introducing XHTML would force web content authors to create more precise documents.

For the most part, this did not happen. In practice, XHTML — along with the three varieties of HTML4, and the wild variation in browser rendering — contributed to the general confusion concerning what was and wasn’t “standard” HTML.

One notable effect of XHTML is the idea that you must “close” empty tags with a trailing slash. If you are in the habit of typing instead of just , you can thank XHTML — it was an XML syntax requirement that all tags must be closed.

General HTML

Start reading below, or use the navigation on the right to jump to a specific topic.

HTML Basics

This section introduces HTML, the language used to author web pages, and provides a little background regarding its history and the reason it is used.

What is HTML?

HTML is Hypertext Markup Language, a format for creating documents and web pages. It was originally invented in the early 1990s by Tim Berners-Lee, and was based on an earlier markup language called SGML (Standard Generalized Markup Language), which was based on an earlier format simply called GML (Generalized Markup Language) developed at IBM in the 1960s.

HTML consists primarily of matching pairs of angle-bracketed tags surrounding human-meaningful text (). The tags provide meaning, context, and display information to the text they surround.

What is a Markup Language?

Imagine any text-based document you have ever read: a website, a book, a PDF, a Word doc, a church bulletin. There is the text, of course — but theres something else: how the text is displayed. Some of the words are larger or smaller, some are italicized or in bold, some are a different color or a different font.

The file that one of these documents is saved into has to contain both the human-readable text and also the information about the display. A number of different ways to accomplish this have been tried, and the most convenient way to do it is to store the information in line with the text itself.

So, for example, if you want to make some text bold or italic, you might do something like this:

Which, in theory, should produce something like:

I want to make these words bold and these other words italic.

These inline matching pairs of style declarations are called tags, and something like this is the basis of almost every markup language. But this format shown above isnt HTML, its just a little made-up example.

The example above has many problems with it, and the inventors of HTML (and SGML and GML) came up with something similar, but much better:

• Square brackets are often used in text, so reserving them for use in tags could cause problems. Instead HTML uses angle brackets: and .
• Writing and over and over is very tedious. HTML simplifies this by using the tag name itself as “start” declaration. The tag name with a slash in front of it ( ) is used as the ending tag.
• Rather than the whole words “bold” and “italic,” HTML uses abbreviations to make it faster to type and less obtrusive to read.

So, taking these things into account, the above example would look like:

I want to make these words bold and these other words italic.

Recently, there has been a move away from explicitly declaring typographical details (like bold and italic) and instead using the markup to convey the meaning, not just the look. Therefore, the and tags are no longer recommended for use. Instead, the preferred tags are and (emphasis). So in contemporary documents the sentence above would be:

I want to make these words stand out and to emphasize these words.

HTML is, at its core, nothing more complicated than a set of defined markup tags.

What is hypertext?

Hypertext is a word that was invented in the 1960s to describe documents that contain links that allow the reader to jump to other places in the document or to another document altogether. These links, which we now take for granted in the modern web, were a big deal when computers were first coming into maturity.

The “hyper” concept of internal and external linking was so revolutionary to the way content is organized on the internet that the word shows up in a number of places:

• HTML is the “HyperText markup language”
• stands for “HyperText Transfer Protocol
• A link from one page to another is called a “hyperlink,” and the data attribute that specifies where a link is pointing to is called a “hyper reference.”

Where and How is HTML used?

HTML is used for almost all web pages. The web page you are reading right now uses HTML. It is the default language of websites.

It can also be used for other types of documents, like ebooks.

HTML documents are rendered by a web browser (the application you are using to read this page). HTML rendering hides all the tags, and changes the display of the rest of the content based on what those tags say it should look like.

Do I need to learn HTML to run my website?

Unless you plan to become a web developer, and build pages from scratch, you don’t need to know all the intricate details of HTML.

If you are just using a blogging platform, a site builder, or a Content Management System (CMS) set up by someone else, you may be able to get by without knowing any HTML — there are “graphic” editors available that make adding content to a blog similar to writing in Microsoft Word or email.

However, sometimes those graphical editors dont work exactly the right way, and sometimes you will want to do something and not understand why you cant. Therefore, it is highly recommended that if you are going to be writing for the web, even just regular blog posts and announcements, that you get a good understanding of basic HTML concepts.

Additionally, there are details of how HTML documents are structured that have an effect on things like Search Engine Optimization (SEO) and data aggregation. If you are interested in staying informed about how your website appears to non-human visitors, understanding HTML is an important skill.

Similarly, website accessibility — the ability for a website to be navigated successfully by people with visual or other handicaps — is an increasingly important consideration. The blind rely on computerized screen readers to translate web sites into sound, and the quality and structure of the underlying HTML document has a big impact on the ability of the screen reader to work properly.

Mostly, HTML is the common underlying language of the contemporary internet. If you want to understand how the world works, it is a good idea to at least have some familiarity with HTML.

Bottom Line on HTML

HTML — Hypertext Markup Language — is the language used for creating web pages and other web-based documents. It consists mainly of matching pairs of angle-bracketed tags, enclosing sections of human-meaningful text. The tags, which are not displayed by web browsers, are used to provide information about how the text and page should be displayed.

HTML Elements and Tags

This section takes a close look at tags, the fundamental building blocks of HTML. It covers how they work, some exceptions to the normal way they work, and a brief discussion on tag attributes.

Structure of Tags

Generally, matching pairs of tags surround the section of text which they affect. Two matching pairs of tags, along with the content they enclose, are called an “element.”

The opening tag can contain additional attributes which provide more information about the contents of the tag and how to display them. These attributes are written as name–value pairs, separated by an equals ( ) sign, with the value placed in quotes.

A few tags do not occur in matching pairs, because they are used to insert something, rather than describe text. These are called “empty” or “void” tags, and the most common one is the one used for inserting an image. The attribute is used to specify the URL of the image.

Notice there is no closing tag, and therefore no enclosed text. The slash right before the final angle bracket ( )is used to “self-close” the tag. This is not absolutely required, but it is a good reminder that whatever follows will not be enclosed. (It is required in XHTML, which will will discuss later in this article.)

There are several other empty tags. Two are fairly straight forward and common.

• inserts a line-break.
• inserts a horizontal rule (line) separator.

Others do not insert something visual, but are used to provide information about the page itself.

Additionally, the tag (which is used to add Javascript to a page) can be empty, but it doesnt have to be.

(More information on , , and tags will be provided later in this guide.)

Block-level vs. inline

With the exception of tags that provide information about the document itself, HTML tags fall into two categories, block and inline.

Block elements

Block elements represent rectangular blocks of content. They have an implied line break before and after. Block elements include sectional content like paragraphs ( ), divisions ( ), and headlines ( , , etc).

It is standard practice to type most block-level tags on individual lines above and below their content:

However, this is not always done, especially with headlines:

Block-level elements can be nested, but some block-level elements can not contain other block-level elements:

Paragraphs and headlines cannot contain other block-level elements.

Inline elements

Inline elements are elements used within text. Bold ( ), italic ( ), and links ( ) are all inline elements.

Inline elements are sometimes called “span-level” elements. There is also a generic span-level element, simply called a span ( ). This doesnt do a whole lot by itself, but can be used to create customized types of text-display, through the use of elements.

(See the section on CSS for information on how to make display in a special format.)

Sometime it doesnt make sense

Images ( ) feel like block-level elements — they are rectangular, have definite dimensions, and are usually displayed outside of the flow of text.

However they are actually inline elements. The reason for this is mostly a hold-over from a less-sophisticated period of web design, but were stuck with it now. The weird implications of this can be avoided easily, but its good to know. (See the section on images and also the one on CSS.)

There are other weird issues like this, and they will be covered later in this guide when they come up.

More about attributes

Almost every element tag can include attributes. Many elements have a specific set of attributes they support (like and the attribute), but there are several elements which are globally supported by all element types.

Two important attribute types are and .

Class attributes

Class attributes are used to mark one or more elements as belonging to a specific “class” or group — this can be used for displaying them all the same way.

For example, it is common to use an unordered list ( ) as a menu, and to make the list item ( ) which points to the current page look different than all the other links in the same list.

An element can have more than one class. Multiple classes are separated by spaces inside the class element.

Because classes are separated by a space, classes may not include spaces in their names.

In CSS, JavaScript, and other languages, the class of an element is notated with a dot before the name.

The above CSS code means that within any element that has a class of , the text color should display as green.

ID attribute

The ID attribute works similarly to the Class attribute, but is conceptually different. Rather than signifying the elements membership in a group, it uniquely identifies that element. For this reason, there can be only one element with any specific ID on any given page.

IDs are less often used for affecting display, and more often used for functional purposes.

IDs can be used for internal linking of a document, such as the Table of Contents on a wikipedia article.

Notice that the links to the sections include the name of the tag, prefixed with the hash or pound sign ( ). This is the standard way to reference the of an element:

Other attributes

Each HTML tag has its own set of available attributes relating to their specific purpose. For example, the tag, which defines a hyperlink, includes the (hyper-reference) attribute, which specifies a URL being linked to.

These attributes will be covered in more detail as we look at each tag individually in later sections.

There are also a number of “global” attributes — attributes any element can have. These will also be covered in more detail later on, as their uses become more relevant.

Comment Tags

The last point to cover in basic HTML tags is the comment. Comments begin with an angle bracket, followed by an exclamation point and two dashes. They end with two dashes and a closing angle-bracket.

Comments may be multi-line.

Comments may not be nested:

You need to watch our for nesting of comments if you ever try to comment-out a large section of existing HTML — inline comments in the original section will mess up your commenting.

Anything inside the comments will not be displayed to the user inside the browser. However, HTML comments can be viewed by the site visitors if they choose to view the page source. Therefore, do not use comments for anything you wish to hide from the public.

What Tags Are Really All About

HTML is essentially text content with tags that are used to specify the meaning of that content within the document and the relationship of each piece of content to the others.

Tags are short snippets of letters inside angle-brackets. They typically consist of a matching pair — an opening and a closing tag. The opening tag is just the tag name, while the closing tag is prefixed with a slash.

Attributes may be added to any element. Attributes are specified inside the opening tag, as name–value pairs joined by an equal sign. The value must be inside single or double quotes (double quptes is standard).

The two most common attributes are the class and id attribute, which are used both for styling and functional purposes.

Textual HTML

This section covers all the most common elements that are used for typographical styling and semantic meaning within the text of a typical HTML document. Elements covered include headlines, paragraphs, lists, and links — and several others.

Headlines

HTML provides six levels of headline elements, through .

When to use and

The tag is considered by Search Engines to be the most important headline on a page, and look to it for a clue as to what the page is about. It should therefore match the content of the tag inside the if at all possible, and their should be only one element on any page.

On your home page and blog index page, it is best to put your site title in the tag, and the titles of articles in a blog index inside tags.

However, on a single-article page, the title of the post or article itself should be inside the tag, with the title of the website in an or even tag.

Similarly on a category-based or tag-based archive page, it is usually best to put the category or tag name inside an tag.

Hierarchical organization

It is (mildly) good for SEO, and very good for readers, to break articles into logical sections and use appropriate heading tags within the content of an article. Heading tags should be used in a hierarchical fashion — if an follows an tag, it should be the header for a subordinate section.

Subtitles

A title with a subtitle should not used two different header tags:

Instead, put the entire title and subtitle into a single headline tag and use another tag to define the relationship:

Headlines on Widgets

Sidebar sections, or widgets, need titles, but these are not generally relevant from a content (SEO) standpoint. Most well-informed designers use tags for this purpose, reserving , , and for keyword-relevant content.

However, if you regularly have so many sub-sections in your page content that you need to use headlines in your main text, theres nothing really bad about using or even in your sidebar titles.

Headlines as link targets

In a particularly long document, it might be a good idea to make it possible to link not just to the page as a whole, but to a specific section.

In the past, only anchor tags ( ) could be used as the target of a link, but that is no longer the case — any element can become the target of a page-location specific link.

The natural candidate for such links are headline tags, because they are used to identify the beginning of sections.

All that is needed to make this work is to add a unique attribute to the header element. Links to that section are simply the page URL, appended with the hash sign ( ) and the ID.

Paragraphs

The paragraph tag — — should surround every paragraph of text in your main content.

Multiple line breaks in your source code (without the line-break tag) will not display as line breaks on-page. In order to get proper display spacing between paragraphs of text, you should use the tag.

Some people prefer to put the opening and closing tags on individual lines. This may help with reading source code, but it makes no difference to how a page ultimately looks to a user.

Many CMSes, like WordPress, insert tags into your post content automatically, so you dont have to worry about it if you are using one of these systems.

Lists

There are three types of lists available in HTML:

• — Unordered list. — Bulleted lists (like this one), called “unordered” because they are not numbered.
• — Ordered list. — Numbered lists, which can use regular numerals (1, 2, 3), roman numerals (I, II, II or i, ii, iii), or letters (A, B, C or a, b, c).
• — Definition list. — A list with individual terms and then descriptions for each term. (This list could have been a definition list, but it isnt.)

Unordered List —

The unordered list is a way to present a list of bullet-pointed items. The list itself is wrapped in the tag, and each item in the list is wrapped in the (list item) tag.

In the past, you could specify what kind of bullet you wanted (disc, square, circle) in the attribute. But as of HTML5, this is not supported. If you want to change the bullets, youll have to use CSS.

Ordered List

Ordered lists are lists which are numbered or lettered. The outside element is , and the tag is used again for each item.

The element supports several attributes which change how the the list is numbered.

The attribute can be used to change the default Arabic numerals (1, 2, 3) to letters or Roman numerals (capitals or lower-case).

Options for are:

• — Arabic numerals (1, 2, 3) — This is the default.
• — Capital letters (A, B, C)
• — Lower-case letters (a, b, c)
• — Capital Roman numerals (I, II, III)
• — Lower-case Roman numerals (i, ii, iii)

The attribute can be used to begin the list numbering on a number other than 1. This can be used for numbers or for other types.

Finally the attribute can be used to number the list items in reverse order. This can be combined with either of the other attributes (or both).

Things to notice about these two examples:

1. The attribute can be negative.
2. Even if the list is , the value is the first number for the list.
3. The attribute doesnt need to specify a value. This is because it has only two possible values: true (present) or false (absent).
4. A top-ten (or similar countdown) list doesnt need to specify a attribute if it ends with 1, which will always be the last number in a reversed list unless otherwise specified. The example above didnt actually contain ten items, so it was necessary to specify.
5. The default behavior is to increase the number for each succeeding list item. Therefore, if you want to “countdown” from a negative number, you should not include the attribute.

Description / Definition Lists

Description lists (or “Definition” lists, as they are more comonly called) are a bit different than ordered and unordered lists. They are used to provide a list of terms with descriptions, such as in a glossary.

The whole list is wrapped in the tag. Each term in the list is marked with a tag (“definition term”), and each term is followed by one or more elements (“definition description”).

The obvious use for a description list is a glossary or dictionary, but that isnt the only standard use.

List of names : with contact information in the description. List of audio track titles : with detailed track information in the description. List of product offerings : with information about the products in the description. List of stats : with the stat name as the term and the stat value in the description

Anytime you have a list of items which each require more detail, the description list is a good idea.

Definition lists are even more powerful than you might already realize because the tag — the description — can hold any other elements: paragraphs, images, other lists. This means that a description list can be a very content-rich markup scheme whenever you have individual items which each need additional details of any kind.

There is also one off-the-wall use for description lists, which is somewhat controversial. It was included as an example in the HTML4 specification, but removed for HTML5: script-like dialogue.

Definition lists are underused, but they are actually a really great way to present all sorts of content.

Nesting lists

All three styles of list can be nested to form an outline-style hierarchical list.

Notice that the bullets automatically change with each nesting. This is the default rendering style for most browsers.

Unfortunately the same thing does not happen with ordered lists. If you want the school-notes outline style with different types of numbering at each level, you have to do it yourself.

Nested lists can mix list types.

It should be noted that lists can not be nested inside of paragraph elements ( ). This is because all lists are block-level elements, and paragraphs (which are blocks also) can only contain span-level elements.

This can occasionally be annoying because in normal written text there are sometimes perfectly good reasons for wanting to include a list inside of a paragraph. However it simply does not work.

Block quotes and inline quotes

If you are quoting someone or something, use one of the two HTML quote elements.

Blockquotes

The blockquote is much more common. This is because of normal typographical convention:

• blockquotes (multi-line quotes or excerpts) are displayed a special way (usually indented and sometimes italicized),
• whereas inline quotes are simply marked with puncutation.

Blockquotes can be used for large blocks of quoted material, whether that material is an excerpt from a literary work, song, another blog post, or an e-mail message that you are responding to.

If you want to cite the source of the quote, there are two ways to do that. The element can be given a attribute, or a byline can be added with a tag surrounding the source title. You can also do both.

It should be noted that that the tag should include the title of the original work being quoted, and may optionally include the name of the author and other information (such as page number or act and scene number).

The citation at the end of the quote could be better identified if it was placed inside of a element, and if the citation itself linked to the source material. Doing this would make the attribute within the tag redundant, so well remove it. Finally, well add a paragraph tag and remove the em-dash (), so that only the information — and not display details — are included.

A blockquote could include a as well, which might be used to introduce the quote itself, or to quote original header information.

Inline Quote

The less-commonly used quoting element is the inline quote, .

This is not often used because there is already a perfectly good way to show that you quoted something — by using quotation marks.

However, using the tag instead of simple quotation marks has a few advantages.

• The display of the quotation marks can be changed via CSS, which is helpful for internationalization, since not all countries use the same symbols for quotation marks.
• The fact that the text is a quotation from another source is semantically clear, whereas quotation marks could be used for other reasons:
  • rhetorical “scare quotes”
  • mentioning a word or phrasing
  • reporting a real conversation that has no source text
• The opportunity to include a attribution linking to the original source of the quote.

Hyperlinks

One of the most important tags in HTML is the anchor tag ( ), which defines a hyperlink. The ability to link documents into a network of connections is the essence of the web, and the definition of “hypertext.”

The element is called an “anchor” because it is used to anchor a linked URL to some specific text on a page. (This is in contrast to the tag, which connects the entire document, not a specific section of text.)

The text inside the element is called the “anchor text,” and the linked URL is specified in the attribute.

Along with the , the tag has several important attributes.

• specifies what window (or browser tab) to open the link in. The default is the same window. If you want to open a new tab set .
• sets the tooltip or hover-text of a link. This displays in a small popup when the user mouses over the anchor text. It is useful for providing some additional information about what the user is about to click on.
• reports on a relationship between the linked document and the current document. It has several possible values:
  • — The linked document has the same content as the current document, but in an alternate format. Used most often to link to RSS feeds.
  • — The linked document is the homepage of profile of the author of the current document or article.
  • — A link to a specific point in the document (such as when creating an on-page table of contents).
  • — The linked document provides help documentation to the current document.
  • — The linked document is the license text for the current document.
  • — The linked document is the next part in a paginated series. Some browsers will pre-fetch the contents of the linked document in order to speed up rendering when the user finally clicks on it.
  • — The linked document is not endorsed by the author of the current document. Used to prevent giving SEO benefit to the linked page. Comment systems often add this to user-entered links by default.
  • — Used to prevent sending referer information in the HTTP request header when the user clicks on the link. Typically, the HTTP request will specify where the user is coming from (the current page). This requests that the browser client omit that information.
  • — Similar to , but without implying an actual sequential relationship. This requests that the browser fetch the contents of the linked page before the user clicks on it, so that navigation to the next page seems instantaneous.
  • — The inverse of , this value specifies that the linked document is the previous page in a paginated series. Some browsers may prefetch the contents.
  • — The linked page provides an interface specifically for searching the current document and related documents.
  • — The linked document provides context as to the topic of the current page.

The attribute is underused by non-technical website creators, and it is a great way to bring rich, semantic information into the markup in a way that search engines, aggregators, and screen readers can understand.

For example: Google uses the link (if linked to a Google+ profile) to display links to other content by the same author in search results. – Google image search includes the ability to search by license, to find Creative Commons licensed content for re-use. That feature depends, in part, on the attribute being used in links to Creative Commons and other open licenses. Several search engines and news aggregation sites use the anchor text and referenced page of a link to determine the topic of a given page.

The tag can also be used in Microformats, which are simple ways of including additional semantic information within existing HTML attributes (usually and ).

For example, the XFN Microformat suggests using the attribute when linking to the home or profile pages of people with whom you have a relationship.

There are several additional Microformats that use the tag, as well as other ways to include this kind of semantic information in the markup of your website. These will be covered in the section on Semantic HTML.

Text decoration

There are a number of simple tags which are used for basic text markup within a paragraph or other element.

Bold

There are two tags that can be used for making text bold.

• is recommended for use to mark “important” text. It causes the wrapped text to display as bold but also carries semantic meaning (that the text itself is somehow important).
• simply bolds the text without suggesting any particular semantic meaning.

Italic

Like bold, there are two ways to make text display in italics.

• suggests that the wrapped text is “emphasized” somehow.
• is simply italicized, with no specific semantic meaning attached.

Underline

Although it has become less popular recently, the standard text display for hyperlinks ( ) is to underline them. Therefore, non-link underlining does not get used very often. There are, though, markup tags for it.

• is the generic tag for underlining text. The use-case presented by the specifications is underlining misspelled words. The HTML5 spec also wants you to know that other elements are usually more appropriate, and dont use this if it could be mistaken for a link.
• means text that has been inserted, and is usually used in conjuction with the tag, to show the changes made to a text.

Line-Through

There are two elements which mark text to be . Each has a slightly different meaning.

• is for text which is to be understood as deleted or changed, and it used with the tag as noted above.
• is used for text which is no longer correct or no longer relevant.

There is also a tag which was available in HTML4.

While the specifications description of and are slightly different in theory, experts have not come to any agreement on the practical details of the difference, or what situations would specifically call for one rather than the other.

Source code and unprocessed text

There are two elements used for displaying text or code which you do not want to be rendered by the browser, but simply displayed “raw” to the used.

• — Is used for blocks of code or unprocessed text.
• — Is used when you need to include a short word or phrase of code inline with your text.

They both display in a monospace font (usually Courier) by default, preserve whitespace, and do not render any tags.

This guide makes heavy use of both the and the elements for displaying source code examples and discussing elements tag names.

Text sizing

You can make text arbitrarily larger or smaller with two elements that otherwise have no specific meaning:

The most common use of sizing elements is placing the subtitle of a page or article into a element nested inside the headline tag.

The generic element

If you need to markup specific length of text for semantic or styling purposes, but none of the existing tags makes sense, you can use the generic element, along with a attribute (and some CSS) to create the desired effect.

Separators

HTML provides two tags for adding in separation within text.

• inserts a line break
• inserts a horizontal line

Neither of these elements requires a closing tag, because they do not enclose any text. If it helps you read your source code better, you may include the self-closing end slash: and .

Line breaks are especially useful when you need to have hard linebreaks but other solutions — like multiple tags dont make sense. Two good examples are poetry or song lyrics and addresses.

This Easier Than It Seems

All this may seem complicated, but it really isnt. Most of the tags you need on a regular basis are easy to remember: headlines, paragraphs, unordered list. You dont need to memorize all the different options or meanings behind each one. Just try to keep in mind that any normal typographical item (like a headline, a list, a paragraph, or a link) probably has an existing HTML tag to accomplish it. If you keep that in mind, you can just write without focusing on these things and then look up the specific items you cant remember.

Try not to get bogged down with options, either. The important thing is that your markup is as meaningful as possible, without being overly complicated. If you cant decide which of two or more options is the best, ask which one is more meaningful. If you cant figure that out, ask which one is simpler. If you still cant decide, just pick one — if they seem that similar, then there probably isnt going to be a huge difference in how it works out.

Structural HTML

This section explains the overall structure of an HTML document, including what types of information are contained in the and . It also explains how to organize the various sections of a typical web page. There will be more information in the HTML5 section below.

Basic HTML Document Structure

HTML documents (web pages) need to follow a few basic structural rules in order to work properly and be read accurately by web browsers.

The document must begin by declaring a DOCTYPE. There are several different HTML (and related) standards that have been in use over the years, and so therefore it is important to specify which type of document (which HTML standard) your document is using.

Mostly, today, the correct DOCTYPE is simply . So an HTML document should begin with:

This isnt exactly an HTML tag in the proper sense, but rather it tells the browser how to interpret all the other tags that follow.

After the DOCTYPE declaration, the opening tag is the tag. The closing of the tag will be the last line of the document.

Inside the HTML tag, you can specify the language of the document (in this case, English).

Nested inside the tag are two sections, the and the . The body contains all the visible content, while the head contains information about the document itself. Nothing is outside of these two sections.

This is the basic structure of every HTML document. Everything is basically extra.

Contents of

The element of an html document usually contains all the information needed by a browser to properly render the document, plus additional information describing the contents (for the benefit of aggregators and bots).

Metadata

The tag is used several times in the to specify various metadata (data about the document).

Metatags are empty tags, requiring no closing tag. You may end them with the self-closing slash ( ), but this is not required (and some people even specifically discourage it).

Character Encoding

There are several different common ways to encode characters (letters, numbers, and punctuation) in computer memory. If you dont specify which one you are using, the web browser may mess up and display some of the wrong characters.

Most of the the time, these days, you want to specify the UTF-8 character set.

(The other common encoding — ASCII — doesnt have all the extended characters like em-dashes and curly-quotes. If youve ever seen weird type glitches where quotation marks or apostrophes have been replaced with seemingly random characters, its because the document was written in UTF-8 but displayed using ASCII — which means someone didnt specify the correct character set in the document.)