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Re: Ways of breaking out of normal interpretation andmeaning

• From: John Cowan <cowan@mercury.ccil.org>
• To: "Costello, Roger L." <costello@mitre.org>
• Date: Sun, 4 Dec 2011 12:33:34 -0500

Costello, Roger L. scripsit:

> In the regular expression language, the dash symbol is a special
> character that means range.  This regular expression says any digit
> from zero to nine:
> 
>     [0-9] 
> 
> By preceding the dash with a backslash:
> 
>     [0\-9]
> 
> we have broken the dash out of its normal meaning and it just becomes
> a meaningless character. The regex now says zero, dash, or nine.

This does work in XML Schema regular expressions, but I don't consider it
a good example, because many other implementations of regular expressions
do not support \-escaping inside character classes.  The conventional way
to write a character class meaning "zero, dash, or nine" is either
"[09-]" or "[-09].

A better example would be "a*", which means "zero or more 'a' characters",
whereas "a\*" means "an 'a' character followed by an '*' character".

-- 
John Cowan                                   cowan@ccil.org
        "You need a change: try Canada"  "You need a change: try China"
                --fortune cookies opened by a couple that I know

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  • Ways of breaking out of normal interpretation and meaning
    • From: "Costello, Roger L." <costello@mitre.org>