[Aaron]

To define a tag, create any ability in the editor. Let's call it Tag Mule, and give it a unique ID of "abTagMule". Then in the upper right, find the blue button which says "Tags". Click on it. In the window which opens, click on "Click to add a new tag". It will add a new entry, with sections for "Tag Group" and "Tag ID". The group is what appears before a "." in a tag, and the ID is the specific tag within that group that appears after the ".". For example, for the tag "Helper.Proficient", the Tag Group is "Helper" and the ID is "Proficient". The dot between the two is neither, and should be omitted here. In this case, enter "AddCompLis" for the Tag Group, and whatever ID seems appropriate for the source of this expanded companion list. For the purpose of this example, we'll use "ExtraCompList".

Now save your file and reload the game system. Once the system has compiled, it will load your file, and because AddCompLis is a dynamic group, Hero lab will now be aware of this tag you've defined called "AddCompLis.ExtraCompList". That's how you define a tag. Note that you could have added the tag definition to any other ability you defined just as easily. Further, note that not all Tag Groups are dynamic.

Alright, on to issue two, adding your newly defined tag to existing races. In the editor, under the general group, the very last sub-tab is called "*Extend Thing". Click on that and you will see that each entry created has 3 sections, for "Thing Unique ID", "Tag Group", and "Tag ID". The latter 2 should be familiar from above, they are where you specify which new tag you want to add to something. "Thing Unique ID" is the target you want to add the tag to.

So for our example, say you wanted this additional companion list to expand the choice to include Mastodons. Look up the ID of the Mastodon animal companion race by going to the appropriate tab in the editor (Race -> Race, Anim Comp), hitting New (Copy), and either filtering the list or scrolling through it to find Mastodon. It looks like that is "anMastadon". Yes, that unique ID has a typo, which is why it's important to look rather than assume.

So, armed with all the pieces we need, go to the Extend Thing tab, create a new entry, enter "anMastadon" for Target Thing ID, "AddCompLis" for Tag Group, and "ExtraCompList" for Tag ID. Save the file and reload the game system, then test to make sure everything is working as expected. I would recommend using a class with a narrow companion list (like Paladin, or Ranger) for testing. Assuming everything works, you just need to add more entries on the Extend Thing tab, one for each race you want to tag with your new Tag.

Clear as mud?