Support of K in regex

Question

The K escape sequence resets the beginning of the match to the current position in the token list (this only affects what is reported as the full match).

What environments/languages/versions support K (keep) in its regular expression engines and what libraries are needed (if any) to use this feature within patterns?

Answer 1

The K escape sequence is supported by several engines, languages or tools, such as:

• boost (since ???)
• grep -P                                                     ← uses PCRE
• Oniguruma (since 5.13.3)
• PCRE (since 7.2)
• Perl (since 5.10.0)
• PHP (since 5.2.4)
• Ruby (since 2.0.0)
• Notepad++ (since 6.0)

...and (so far) not supported by:

• .NET
• awk
• bash
• ICU
• Java
• Javascript
• Objective-C
• POSIX
• Python
• Qt/QRegExp
• sed
• Tcl
• vim        ← it doesn't have K, but its zs is equivalent
• XML
• XPath