Make file and directory names lowercase. In general, separate words with hyphens, not underscores. Use only standard ASCII alphanumeric characters in file and directory names.
Exceptions for consistency
If you're adding to a directory where everything else already uses underscores, and it's not feasible to change everything to hyphens, it's okay to use underscores to stay consistent.
For example, if the directory already has
lesson_3.jd, it's okay to add your
new file as
lesson_4.jd instead of
However, in all other situations, use hyphens.
It's okay to have some inconsistency in filenames if it can't otherwise be avoided. For example, sometimes tools that generate reference documentation produce file names based on different style requirements or based on the design and naming conventions of the product or API itself. In those cases, it's okay to make exceptions for those files.