php - Regex - Convert HTML to valid XML tag

I need help writing a regex function that converts HTML string to a valid XML tag name. Ex: It takes a string and does the following:

• If an alphabet or underscore occurs in the string, it keeps it


• If any other character occurs, it's removed from the output string.


• If any other character occurs between words or letters, it's replaced with an Underscore.

Ex:
Input: Date Created
Ouput: Date_Created

Input: Date
Created
Output: Date_Created

Input: Date\nCreated

Output: Date_Created

Input: Date    1 2 3 Created
Output: Date_Created

Basically the regex function should convert the HTML string to a valid XML tag.

Answer

A bit of regex and a bit of standard functions:

function mystrip($s)
{
        // add spaces around angle brackets to separate tag-like parts
        // e.g. "
" becomes " 
 "
        // then let strip_tags take care of removing html tags
        $s = strip_tags(str_replace(array('<', '>'), array(' <', '> '), $s));

        // any sequence of characters that are not alphabet or underscore
        // gets replaced by a single underscore

        return preg_replace('/[^a-z_]+/i', '_', $s);
}