You want a regex that matches both single-line and multiline comments, as described in the "Problem" sections of the preceding two recipes.

(?-s://.*)|(?s:/*.*?*/)

(?-m://.*)|(?m:/*.*?*/)

//[^
]*|/*.*?*/

//.*|/*[sS]*?*/

You might think that you could just use alternation to combine the solutions from the previous two recipes: //.*|/*.*?*/. That won’t work, because the first alternative should have “dot matches line breaks” turned off, whereas the second alternative should have it turned on. If you want to combine the two regular expressions using the dot, you need to use mode modifiers to turn on the option “dot matches line breaks” for the second half of the regular expression. The solutions shown here also explicitly turn off the option for the first half of the regular expression. Strictly speaking, this isn’t necessary, but it makes things more obvious and prevents mistakes with the “dot matches line breaks” option if this regex were combined into an even longer regex.

Python and JavaScript (with or without XRegExp) do not support mode modifiers in the middle of the regular expression. For Python and JavaScript with XRegExp, we can use the negated character class ‹[^ ]*› to match everything up to the end of the line for the single-line comment, and use ‹.*?› for the multiline comment with “dot matches line breaks” turned on.

JavaScript without XRegExp does not have an option to make the dot match line breaks. So we keep ‹.*› for the single-line comment, and we use ‹[sS]*?› for the multiline comment.

Recipe 2.4 explains the dot, including the mode modifiers that affect it, and the workaround for JavaScript. Recipe 2.8 explains alternation.