What do names for "To..." phrases do?

Authoring Inform 7
1

In the Standard Rules, you can see things like:

To decide which real number is the absolute value of (R - a real number) (documented at ph_absolutevalue) (this is the abs function): (- REAL_NUMBER_TY_Abs({R}) -).

What is the purpose of the “(this is the abs function)” part? I know you can name rules like this, but there don’t seem to be any mentions in the documentation about naming phrases. Can the name be used in some manner?

2

This lets you store a reference to the phrase in a phrase variable. This is described in chapter 22.

The func-global is a phrase real numbers -> real numbers variable.

When play begins:
	let func-global be the sin function;
	say "[func-global applied to -0.5].";
	let func-global be the abs function;
	say "[func-global applied to -0.5].";
3

It’s also important for use in equations, where it allows expressions like “sin(x)” and “abs(x)”.