[web-annotation] Issue: (model) vague definition of charactor position for text position selector marked as i18n-review

r12a has just labeled an issue for 
https://github.com/w3c/web-annotation as "i18n-review":

== (model) vague definition of charactor position for text position 
selector ==
The [text position 
selector](https://www.w3.org/TR/annotation-model/#text-position-selector)
 spec doesn't define the exact meaning of the term "character 
position".

There are many possible definitions. "character position" might be 
measured in units of UTF code points, UTF-8 code units, UTF-16 code 
units etc.

Interoperability issues will result if different implementations 
assume incompatible meanings.

See https://github.com/w3c/web-annotation/issues/206