Positive lookbehind and \R in a regular expression

[guinness]

Could someone please explain why R in a positive lookbehind is not working?

#include <Array.au3>

Local $sData = FileRead(@ScriptFullPath)
Local $aArray = StringRegExp($sData, '(?ims)(^Func(?=\h)\h+(\w+)\h*\(.*?(?<=\R)EndFunc(?=\h))', 3) ; (?<=\R) does not work!
_ArrayDisplay($aArray, 'SRE 1')

$aArray = StringRegExp($sData, '(?ims)(^Func(?=\h)\h+(\w+)\h*\(.*?(?<=\r|\n|\r\n)EndFunc(?=\h))', 3) ; (?<=\r|\n|\r\n) does work!
_ArrayDisplay($aArray, 'SRE 2')

Func Example()
    Return True
EndFunc   ;==>Example

Func SomeFunc($vVar)
    Return $vVar
EndFunc   ;==>SomeFunc

[mikell]

From the PCREpattern bible

In a UTF mode, PCRE does not allow the C escape (which matches a single data unit even in a UTF mode) to appear in lookbehind assertions, because it makes it impossible to calculate the length of the lookbehind. The X and R escapes, which can match different numbers of data units, are also not permitted.

Edit

On the other hand, this works :

Local $aArray = StringRegExp($sData, '(?ims)(^Func(?=\h)\h+(\w+)\h*\(.*?\K(?:\R)EndFunc(?=\h))', 3)

Edited December 22, 2013 by mikell

[guinness]

Suppose I should have read the docs before posting. Thanks mikell.