...which obviously does not exist. Several escape sequences actually produce some effect, such as \n for a new line, and \t for a tab, though WoW ignores these in many contexts (eg. newline characters in chat messages are ignored).
To avoid this issue with file paths, you can either escape your backslashes by adding a second backslash in front of each one, as in my example above, or you can use doubled square brackets instead of quote marks to enclose your string, as in:
Looking at other addons that use the library is generally a better idea than trying to find documentation about the library. WoW library authors tend to either write no documentation at all, or use Luadoc to auto-generate documentation from comments in the code, which usually results in documentation that reads like something BabelFish might have spit out in 1995. :(