Appending a single category to the end of a page is of limited use. An editor of an outline would then need to cut and paste the list to its final resting place in the outline. Then the process would need to be repeated for every blank or missing section. A single outline could have several dozen of these. A new outline skeleton could have over a hundred. Fetching categories one-at-a-time using the prototype tool would be extremely time consuming.
But, the tool you built reveals the potential of things to come.
The method could be applied to building large outlines very rapidly.
Step one: The user builds the heading structure for a new outline.
Step two: The user places a tag (in the form of a hidden comment) in each empty section indicating the category intended to populate that section.
Step three: The user runs the FetchCats tool to process the outline. It reads the first tag, fetches the category indicated, and inserts the entire list of articles (article namespace only) from that category into that section of the outline, repeating this process for each tag.
Step four: The user smiles at a job well done. Note, that the tags are not removed, as they can be used later to update the sections.
The tool I'm interested in is the one described in Step three and four above.