`matches` function doesn't work with flags argument

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trafficstars

according to the xpath 3.0 spec, the matches function can take a third argument for regex flags.

however this doesn't seem to work in fontoxpath:

1: //tip[matches(., "^You", "m")]
         ^^^^^^^^^^^^^^^^^^^^^^^

Error: XPST0017: Function Q{http://www.w3.org/2005/xpath-functions}matches with arity of 3 not registered. Did you mean "Q{http://www.w3.org/2005/xpath-functions}matches (xs:string?, xs:string)"?
  at <functionCallExpr>:1:7 - 1:30
  at <pathExpr>:1:1 - 1:31

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