how does COMMAND_CONFIG work for other generators?

the documentation has new generator expression OUTPUT_CONFIG and COMMAND_CONFIG. I am not familiar with Ninja, it seems like it supports configuration files for file-level dependencies. I am mostly interested in this part:

With other generators, the content of ... is evaluated normally.

(where ... is part of $<OUTPUT_CONFIG:...>). How does this expression behave for other generators?

@kyle.edwards