What LanX said. Do not do it with regex.

Your regex is wrong (besides what LanX noted) in that it is extremely unsafe and misses some restrictions.

my @numbers = m{
    <stlib:membit       # Opening tag
    [^.]*               # Optional attributes
    >                   # End of opening tag
    \s*                 # Optional whitespace
    ([0-9]+)            # The number you want
    \s*                 # Optional whitespace
    </stlib:membit>     # Closing tag
    }gx;                # I want all of them in this line
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