Supply a warning for using \K and instead suggest <(

or )>

src/QRegex/P6Regex/Grammar.nqp

@@ -372,6 +372,9 @@ grammar QRegex::P6Regex::Grammar is HLL::Grammar {
         ~ ' If you meant the backspace character, quote it ("\b") or use it as'
         ~ ' inside a character class (<[\b]>)'
     >}
+    token backslash:sym<K> { 'K' <.obs:
+        '\\K', '<( for discarding text before the capture marker or )> for discarding text after.'
+    >}
     token backslash:sym<A> { 'A' <.obs: '\\A as beginning-of-string matcher', '^'> }
     token backslash:sym<z> { 'z' <.obs: '\\z as end-of-string matcher', '$'> }
     token backslash:sym<Z> { 'Z' <.obs: '\\Z as end-of-string matcher', '\\n?$'> }