Create gesellschaft-fur-popularmusikforschung.csl

Sorry, I am a very newcomer in editing styles. I want to create a new style called "Gesellschaft für Popularmusikforschung (German)" by editing "harvard 7 de", because this style is quite similar to my needs. 

I didn’t manage to solve the following options:

-	Subject: position of editor names in bibliographic entries of an edited book, annual or conference proceedings:

a.	What I managed: entry of a single book chapter or paper-conference, e.g.: 

Helms, Dietrich (2008). "What's the difference? Populäre Musik im System des Pop." In: PopMusicology. Perspektiven der Popmusikwissenschaft. (The latter titel is in italics!) Hg. von Christian Bielefeldt u. Udo Dahmen u. Rolf Großmann. Bielefeld: Transcript.


b.	What I didn’t manage: entry of the whole edited book, e.g.:

Bielefeldt, Christian et. al. (Hgg.) (2008): PopMusicology. Perspektiven der Popmusikwissenschaft. (The latter titel is in italics!) Bielefeld: Transcript.


-	Subject: If container titles contain more than 2 editor names, the delimiter „u.“ should only divide the last 2 editor names. All names before should be devided by a comma (,).

c.	Wrong: 
Hg. von Christian Bielefeldt u. Udo Dahmen u. Rolf Großmann.

d.	True:
Hg. von Christian Bielefeldt, Udo Dahmen u. Rolf Großmann.

-	Subject: Text formatting of the „labels“ within the category „names“ in container titles: I selected the form „verb-short“. There appeares the text: „Hg. von“. I want to alter it into „Hg. v.“. Is that possible? 

-	Subject: Text formatting of the „et. al.“ within the category „names“ in container titles. There appeares the german text: „u. a.“. I want to alter it into „et. al.“. Is that possible?


My motivation of creating this citation style: I am member of the „Gesellschaft für Popularmusikforschung“. The chairman of it had allowed me to create this style regarding their citation standards. If I will have managed all technical (and validation) problems the chairman of course wants to check my edition. 

Here you will find the citation standards of GfPM (Gesellschaft für Popularmusikforschung) which I tried to implement in my edition: http://www.aspm-samples.de/hinweise.html

I am looking forward to beeing supported in my edition in any way! Thanks a lot! 


this is, btw. exactly what @zuphilip was suggesting here:
https://github.com/citation-style-language/styles/pull/1221#issuecomment-62065772