You cannot do this in WP5 documents. Here the HyperBegin pair prefix any text with the HTML anchor . The BookMark pair surround any bookmark text. The first of the pair, BookMark, is passed the bookmark name. Note how this is used to constuct the HTML anchor.
Some users wish to constuct indices from tagged entries in the documents.
To handle this, we need to do two things. First to detect index marks, inserted into the WP document. Second to collect these index entries, sort them and format them. If we keep these processes separate, then they can be applied to any number of files. In this release we detect the Index entry.