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.