Code size: Very small
Documentation: Very little - more would probably be needed for those not familiar with PHP.
Ease of use: There is just 1 file, so it is fairly easy if you are lucky to have it work on your system. You might need knowledge of PHP to edit the default variable values though.
Options: In the script you select the directory ($path) of the files to view, and edit the array ($secure) of file exceptions.
How to call the script: Enter URL of script with file parameter, e.g.,
Comments: It is very buggy on some systems (especially Windows). For example, it is supposed to print line numbers inline with code, but it only printed a "1" for the first line on my system.