I have not yet seen this double-hyphen explained, which is written eg. in *An Etymological Dictionary Of The Hittite Inherited Lexicon* (Kloekhorsts 2007)

> 
> *-a* (3rd.sg.pres.midd.-ending): see *-a(ri)*
> 
> 
> *=a* 'and, too': see \*=(i̯)a
> 
> 
> *=a* 'but': see *=(m)a*
> 
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> *=a-* (enclitic pronoun) 'he, she, it': […; pg. 196-198]
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> 
> 

What's the difference from *=* to the usual hyphenation marking morpheme boundaries?

> 
> […] The forms *[n]=e-e=n* (KBo 17.1 KBo 25.3 i 20 (OS)) and *[n=e-e=]n* (StBoT 25.4 i 15 (OS)) seem to show that […; pg. 208-209]
> 
> 
> 

Wow, that's most cryptic. The question should be however easy to answer without detours into grammar (otherwise, pending own research, I would revise the question). Is the difference just *ending* versus *enclitic*?

How specialized is this, certainly not exclusive to Hittite studies?!