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