Player name and Understanding

I’m new to making IF and Inform 7 is pretty neat but I’ve come up against a wall that I can’t figure out. Using the example in the documentation, I’ve got it setup so that it changes the command prompt to ask for the player to enter a name and when they do it assigns the first word to [player’s firstname] and the whole name to [player’s fullname] as indexed text.

The problem I’m coming across is I want Inform to understand that when the player puts in a command that includes either of those values to know that it is referring to the player themselves. I’ve tried something like:

Understand "[player's firstname]" and "[player's fullname]" as the "[player]"

but I just get errors about it not understanding the phrase. I was hoping it’d work like the examples in the documentation and yet it doesn’t. I’ve searched around online but can’t seem to find an answer to it (if there is one). Any help would be appreciated.

Check out example 408, “Fido.” If you’ve got the part that assigns the names working to your satisfaction, the code in there (specifically the business around “Understand the nickname property as describing the dog.”) looks like it should do what you want.