Hi.

In analising some HTML using using regexps, I need to match HTML tags containing certain attributes independently of the order in which these attributes appear -- but ensuring that each of the attributes appears once.

To do this, I would need a reasonably concise and efficient way to build:

from two regexps X and Y, a regexp almost equivalent to 

    XY|YX

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from three regexps X, Y and Z, a regexp almost equivalent to 

    XYZ|XZY|YXZ|YZX|ZXY|ZYX

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... you see the pattern. The "almost" refers to the fact that I would like captured groups in X, Y, Z to be accessible as if only the first case in the alternate (|) construct was there.

I'm currently using 

    (?:X|Y){2}    (?# for the first example)
    (?:X|Y|Z){3}  (?# for the second)

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which is very very close to what I need --and works well for my particular job-- but is not formally correct, since it would give a false positive if any of the subexpressions X, Y, Z were matched twice.

Is there any way to 'burn out' those X, Y, Z so that they can only match once? I could use something in the lines of: 

(?:(?(1)NOTMATCH|(X))|(?(2)NOTMATCH|(Y))|(?(3)NOTMATCH|(Z))){3}

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where NOTMATCH is a regexp that never matches. But it gets unmanageable if X, Y, Z contain capture groups.

Note that this is a problem I often run against when using regexps -- not only in the context of analising HTML. Would it make sense to extend regexp syntax to include a combining operator (like XY or X|Y) meaning 'match these in sequence but in any order?' e.g. X&Y?

All comments welcome.

In reply to Operator for "these expressions, in any order" by jsalvata

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