STViz tool issue

With the latest GH code the STViz tool (triggered via the `-XdbgST` parameter) shows unusual selection ranges in the source code for a `RuleFunction` entry:

Selection begins a couple of lines too early and ends early as well. Seems to be a pure problem of the STViz tool, not the ST generation.

Start by reproducing the issue in the STViz tool using the -XdbgST parameter with a RuleFunction entry from the latest code. Inspect how STViz determines the source selection range and compare it with the displayed source; done means the selection starts and ends at the RuleFunction's actual range.

Written by the indexing model from the issue text.