.required field prompting command pane

The following snippet of code from a state rule workflow is pulling up the command window with the command prompt autofilled with an unknown command.

...
State Assigned {
on Actions [always] do {
comments.required ("Tasks moved to Actions state require comments regarding move.");
} transit to Actions
....

Moving a task without comments brings up the command window with the command bar autofilled with "Actions comments" of which "comments" is an 'unknown command'. What? First, why does it bring up the command prompt, is that default for the .required condition (not explained at all in the Workflow language quick reference). Second, what is designating the autofill to include "Actions comments"

As a workaround, in the interim, I have changed the display message to include instructions to remove "comments" from the command bar and to insert text into the comment window; then select apply which completes the desired action but is not pretty.

I was trying an "assert comments.isNotEmpty" command but the <message> was not displaying in the blue panel and instead stated "Bad Request"