19.2.2.5 Common Case in Pathname Components

For the functions in Figure~19–2, 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.