Base Directory Specification - XDG_*_DIRS syntax

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The XDG Base Directory Specification states that the environment variables  
$XDG_DATA_DIRS and $XDG_CONFIG_DIRS both have a list of paths that are  
separated by a colon (':') character. How should the values be interpreted  
if the path contains colons? Should the colon be escaped? How about the  
escape character, should that be escaped then too (e.g. '\\')? Or are  
colons allowed in the path at all?