Can anyone explain what $extension.path holds in redwood layout?

Summary:

Can anyone explain what $extension.path holds in redwood layout?

Content (please ensure you mask any confidential information):

We are having requirement to make few fields readonly when we are creating records from smart action of any of parent objects link Account, Contact etc as those will be autopopulated. But we don't want that to be readonly when they are creating from the object itself.

So we are checking if this $extension.path could here in requirement.

Version (include the version you are using, if applicable):

25B

Code Snippet (add any code snippets that support your topic, if applicable):