Some character or set of characters is desirable to separate fields. In this file naming convention, a hierarchy of (non-alphanumeric) delimiter characters is defined, organized in decreasing order of magnitude at least three levels deep, with alternative characters defined for each level (to avoid operating system pickiness).
Many operating systems divide up file names into a name-part and an extension separated by a character such as a period. Therefore, we define the Level-0 delimiter as that character which separates between a file name proper and a file extension or type). The first choice for this character is whatever the operating system uses (a period for MS-DOS and VMS, a space for CMS, etc.). If an operating system does not use extensions, then a period should be used.
Level-1 delimiters are used for padding and as optional
field separators. The first choice is the underscore
character (``_''). If this is unavailable,
the dash or hyphen character (``-'') may be used.
Level-2 delimiters are used as decimal points. Periods may
not be used in most situations, since they are the Level-0
delimiters in many environments. Instead, the first choice
is the dollar sign (``$''), with the percent sign (``%'') used
as an alternate.
Note that Level-0 delimiters are required, while Level-1 delimiters are used to improve readability where the operating system allows longer file names. Level-2 delimiters may be used where needed.