Editor: Count characters in xml but without some tags

Hi guys,

we need to count the characters (including spaces) within a xml, but without counting the characters of some specific xml-tags, which e.g. includes meta-information. 

My idea was to begin from the root element and go forward until end and count with the command length:

length(oid_xpath_string(oid_caret(),"."))

But i have problems with the count with nested xml-tags.

Maybe you guys had the same requirement and can help me. 

Thank you in advance.

Greetings from germany