Substitutes strings of the form

     (::|..)(++|--|øø)<counterName>

inside text lines and attribute values by string value of the counter, while incrementing/decrementing counters along the way.

The counter must have initialized by the time it’s used or else a DesugaringError will occur.

E.g., here is a correct use of a counter:

<> Chapter counter=SectionCounter <> Section number=::–SectionCounter

After the desugarer is run, this would become:

<> Chapter counter=SectionCounter <> Section number=-1

The second capturing group (++|–|øø) determines whether a counter is incremented, decremented, or kept equal at a point (according to its step size), whereas the first capturing group determines the string value of the counter is echoed ‘::’ or silenced ‘..’, i.e., inserted or not into the document at that point. In partuclar, a counter of the form

   ..øø<counterName>

has no effect on the document.