Another use case could be, that you are simply not
interested in postings about christmas.
- /christmas([-_ ]?(?:tree|time|eve|pudding))?/
+ /christmas(?:[-_ ]?(?:tree|time|eve|pudding))?/
ATTENTION:
It is absolutely important, that you use grouping
-parantheses instead of capturing parantheses!!
+parentheses instead of capturing parentheses!!
-Grouping parantheses are:
+Grouping parentheses are:
(?: )
-If you use capturing parantheses, which are
+If you use capturing parentheses, which are
( )