In CGEL, in the section on "supplements", there is a short subsection on "indicators" (pages 1354 and 1355). These are defined as follows: "Supplements may contain indicators which serve to clarify the nature of their semantic relation to the anchor." Four examples are given and the function is said to be a "specifying" one. It is not made explicit whether this is the only function or just one of many. The examples given are "namely", "that is", "for example" and "especially". Semantically, all represent an includer/included function (X namely Y, X for example Y and X particularly Y) and are best exemplified with appositives (specifying noun phrases):
The interviewee, namely Jane, is here.
But one can say that another includer/included function is a general X including Y:
Everyone, even Jane, is here.
Is "even" an indicator? If it is, what about other degree adverbs, with other types of supplements:
Jane left the room, practically running out.
Is "practically" an indicator? Or, if a focusing adverb like "especially" is an indicator, what about a modality adverb like "probably" (here with another type of supplement):
Jane, probably angry at the fact, left the room.
Or, going back to what I presume is a specifying noun phrase:
Someone, probably Jane, is here.
To sum, the question is: Could any adverb beginning a supplement be considered an indicator? If not, then what is an indicator in more precise terms?