Common Case in Pathname Components

19.2 Pathnames

19.2.2 Interpreting Pathname Component Values

19.2.2.1 Strings in Component Values

19.2.2.1.2 Case in Pathname Components

19.2.2.1.2.2 Common Case in Pathname Components

For the functions in Figure 19.2.2.1.2 Case in Pathname Components, a value of :common for the :case argument that these functions should receive and yield strings in component values according to the following conventions:

All uppercase means to use a file system's customary case.
All lowercase means to use the opposite of the customary case.
Mixed case represents itself.

Note that these conventions have been chosen in such a way that translation from :local to :common and back to :local is information-preserving.