you need to assign a name to the regular expression so that $RegEx() knows to store the matches, and $RegML() knows where to fetch them from. Your $RegML() parameters are also incorrect. The following should work:

if ($regex(Junk, $1-,/\b(string|string1)\b/gi)) { echo -a STRING WAS: $regml(Junk, 1) }

Note: Since you're using the /g flag, you may get more than one match, so you may want to loop the $RegML() results.