When you encounter a new command, I
strongly recommend that you consult
both the
online version of the comref and also the
Unofficial comref. There you will learn the syntax, and often find helpful tips and examples. Following this procedure will save much time and frustration. There are other version of the comref, and some people like to use those too.
If you're still not clear on how to use a command, check the searchable FAQ in the Editors Depot and use the forum search function.
There is a tutorial in the Ed Depot which explains the mysteries of "this" and "_this".
And if all else fails, post a question.
