Regex to match a CSS class name

I am trying to write a regex that matches a valid CSS class name structure. I have this so far:

$pattern = "([A-Za-z]*\.[A-Za-z]+\s*{)";

$regex = preg_match_all($pattern, $html, $matches);

However, a class name can be in the following formats that my regex won't match:

p.my_class{
}
p.thisclas45{
}

These are just some cases, I've looked around to find the rules of how you can name a class in a style block but couldn't find anything. Anyone know where the rules for the class naming conventi开发者_如何转开发ons are?

Are there any more cases that I need to consider? What regex would you use to match a class name?

I have already narrowed it down to a style block using the PHP DOM Document class.

Have a look at http://www.w3.org/TR/CSS21/grammar.html#scanner

According to this grammar and the post Which characters are valid in CSS class names/selectors? this should be the right pattern to scan for css classes:

\.-?[_a-zA-Z]+[_a-zA-Z0-9-]*\s*\{

Note: Tag names are not required as prefix for classes in css. Just .hello { border: 1; } is also valid.

This regex:

/(\w+)?(\s*>\s*)?(#\w+)?\s*(\.\w+)?\s*{/gm

will match any of the following:

p.my_class{}
p.thisclas45{}
.simple_class{}
tag#id.class{}
tag > #id{}

You can play around with it, on RegExr, here.