I need to rewrite index.htm and index.html to index.php... and nothing else... this seems to work, but I just want to make sure there won't be any unexpected results...
index.htm|index.html
The dot stands for "any character" -> e.g. index2htm or index-htm match.
I'm not sure how the apache regular expressions are implemented but if possible you should avoid long branches, esp. when they are almost identical. I'd rather use