add a new property to detect tags that may be (or MUST be) used as Wref's

[kosloot]

In the code for folia.py and libfolia, there are several places where we have to check if a Word, Phoneme or Morpheme is to be handled special, e.g. as a Wref.

Examples: (folia.py)

            if isinstance(child, (Word, Morpheme, Phoneme)):
                #Include REFERENCES to word items instead of word items themselves
                attribs['{' + NSFOLIA + '}id'] = child.id

            if isinstance(c,Word) or isinstance(c,Morpheme) or isinstance(c, Phoneme):
                targets.append(c)

                if type is layerclass:
                    for e2 in layer.select(AbstractSpanAnnotation,set,True, (True, Word, Morpheme)):
                        if not isinstance(e2, AbstractSpanRole) and self in e2.wrefs():
                            yield e2

(in the latter case I even wonder if Phoneme is missing there?)

Examples from folia_impl.cxx

    for ( const auto& el : data ) {
      if ( ( el->element_id() == Word_t ||
	     el->element_id() == Phoneme_t ||
	     el->element_id() == Morpheme_t )
	   && el->refcount() > 0 ){
	xmlNode *t = XmlNewNode( foliaNs(), "wref" );

    if ( c->parent() &&
	 !( c->element_id() == WordReference_t
	    || c->element_id() == Word_t
	    || c->element_id() == Morpheme_t
	    || c->element_id() == Phoneme_t ) ) {

etc.

Maybe it is a good idea to create a property to select those special cases, where Word, Morpheme and Phoneme have a property REFERABLE, or such. It makes the code clearer, faster and more robust.

[proycon]

That's a good idea indeed, I'll think of something.

[proycon]

I added a property that will be called WREFABLE in the C++ code.