%
    ^
    \s*
    (                               # <1>
        # Single tags like <foo/>
        <
        \s*
        [a-zA-Z:]+
        (?:
            \s*[a-zA-Z:]*
            \s* = \s*
            (?:'[^']*'|"[^"]*")
        )*
        \s*
        /\s*
        >
    |
        # Tags in pairs like <foo>content</foo>
        <
        \s*
        ([a-zA-Z:]+)                # <2/>
        (?:
            \s*[a-zA-Z:]*
            \s* = \s*
            (?:'[^']*'|"[^"]*")
        )*
        \s*
        >

        (?:[^<>]* | (?1))*

        <\s*/\s*\2\s*>
    )                               # </1>
    \s*
    $
%x