The LIST macro serves as a tag for the particular directory level that the makefile is found in.
The LIST macro can contain a list of names that are separated by spaces. This is used when we squash directory levels together; see "Advanced Topics," later in this chapter.
Here are the common values corresponding to the directory levels:
Note that you're free to define whatever values you wish — these are simply conventions that we've adopted for the three directory levels specified. See the section on "More uses for LIST," below.
Once the directory has been identified via a tag in the makefile, you can specifically exclude or include the directory and its descendants in a make invocation. See "Performing partial builds," below.