HTML 5 Draft Standard - 30 July 2009 - Huihoo

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Note: Implementors are strongly urged to carefully examine any third-party
libraries they might consider using to implement the parsing of syntaxes
described below. For example, date libraries are likely to implement error
handling behavior that differs from what is required in this specification, since
error-handling behavior is often not defined in specifications that describe
date syntaxes similar to those used in this specification, and thus
implementations tend to vary greatly in how they handle errors.
2.4.1 Common parser idioms
The space characters, for the purposes of this specification, are U+0020 SPACE, U+0009
CHARACTER TABULATION (tab), U+000A LINE FEED (LF), U+000C FORM FEED (FF), and U+000D
CARRIAGE RETURN (CR).
The White_Space characters are those that have the Unicode property "White_Space".
[UNICODE]
The alphanumeric ASCII characters are those in the ranges U+0030 DIGIT ZERO .. U+0039
DIGIT NINE, U+0041 LATIN CAPITAL LETTER A .. U+005A LATIN CAPITAL LETTER Z, U+0061
LATIN SMALL LETTER A .. U+007A LATIN SMALL LETTER Z.
Some of the micro-parsers described below follow the pattern of having an input variable that
holds the string being parsed, and having a position variable pointing at the next character to
parse in input.
For parsers based on this pattern, a step that requires the user agent to collect a sequence of
characters means that the following algorithm must be run, with characters being the set of
characters that can be collected:
1. Let input and position be the same variables as those of the same name in the algorithm
that invoked these steps.
2. Let result be the empty string.
3. While position doesn't point past the end of input and the character at position is one of
the characters, append that character to the end of result and advance position to the
next character in input.
4. Return result.
The step skip whitespace means that the user agent must collect a sequence of characters
(page 42) that are space characters (page 42). The step skip White_Space characters means
that the user agent must collect a sequence of characters (page 42) that are White_Space (page
42) characters. In both cases, the collected characters are not used. [UNICODE]
When a user agent is to strip line breaks from a string, the user agent must remove any
U+000A LINE FEED (LF) and U+000D CARRIAGE RETURN (CR) characters from that string.
The code-point length of a string is the number of Unicode code points in that string.