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This document serves a rationale document for various parts of the HTML5 specification. Over time this page will be a complete rationale document.

General Rationale

One Vendor, One Veto

Part of the the goal of the WHATWG is to document how web browsers actually handle HTML. As such browser vendors already have veto power - by not following the standard. The W3C and WHATWG do not have any enforcement power and can only write what browsers are willing to implement. Not removing features from the HTML standard that at least one browser vendor has stated they are unwilling to implement causes the HTML spec to not accurately document reality.[1][2]

Specific Elements


the <plaintext> element is a obsolete precursor to the <pre> element. [3] It is is now in the HTML5 spec as a method of stopping all further html token parsing. It lacks an end tag and just emits the rest of the page as plain text. It throws a parse error upon reaching the end of the document as it is not considered a valid element (and it is missing an end-tag).


<image> element is treated as an alternate (but invalid) name for <img>. This is because some sites (around 0.2%[4]) make this mistake. It is already treated as an image by most major browsers.

Meter and Progress (are not the same thing)

<meter> is not just a special case of <progress>. The meter element represents a scalar measurement within a known range, such as storage quota usage, a relative popularity rating or relevance indicator. The control allows for the indication of high and low ranges, or minimum, maximum and optimal levels.

The progress element, on the other hand, represents the completion progress of a task. This could be a real time indicator for background processing task (e.g. using Web Workers or a file upload). Progress elmements can also be in the indeterminate state, indicating that something is in progress, but it's completion progress is unknown.

The default rendering for a meter element could look something like the following:

example of proper rendering for the meter element

Whereas, the default rendering for the progress element could look like this:

Alternatively, an indeterminate progress bar could also be styled as a throbber, which indicates progress without any indication of the remaining progress:

picture of the default apple throbber

See Re: <progress> draft for details.

B, I, EM, and STRONG

<em> is meant to indicate that some text is emphasized. <strong> is meant to confer importance upon text. <b> is meant for text that is stylistically offset from the rest of the text. Finally <i> is used to indicate that some text is meant to be read in an alternate mood.

For example

   Cats are <em>cute</em> animals.

could mean that cats are specifically cute.

   Cats are <strong>cute</strong> animals.

could mean that the word cute is in some way important

   Cats are <b>cute</b> animals.

could mean that the word cute is a new word (perhaps in a language lesson) but is not important

   Cats are <i>cute</i> animals.

could mean that the word cute is meant to be read in a different tone (sarcastically for example)

IMG tag & alt text

On certain types of pages adding alt text is impossible (like sites that the user could upload images but does not supply a description). Because of this the alt attribute is optional [5][6]

HTML parsing

script element

Why the restrictions for contents of script elements? Why the complicated parsing rules for script elements?

See http://lists.w3.org/Archives/Public/public-html-comments/2010Mar/0017.html

quirks mode

The HTML parser has the following behavior difference in quirks mode:

A start tag whose tag name is "table"
If the Document is not set to quirks mode, and the stack of open elements has a p element in scope, then act as if an end tag with the tag name "p" had been seen.

Why? See http://hsivonen.iki.fi/last-html-quirk/

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