One of the most important, and unfortunately subtle, concepts in Agar is that of the file-mask. Every rubric test has an associated ``file-mask'' field. When the tests are run, each file of each submission is compared against the file-mask for each test5.3. Any files that match are given to an invocation of the test. Depending on the settings for an individual test, points will may awarded if any invocation of a test for a submission passes or only if all invocations of a test for a submission are successful. If no files in a submission match the file-mask for a specific test, then no points are awarded.
Agar supports the concept of a ``Default File-Mask'', which is automatically set on startup if the Startup Wizard is utilized. For example, if the ``C/C++ Code'' option is utilized, the default file-mask is set to ``*.c, *.cc, *.cpp, *.C, *.h''. Any tool whose file-mask is not explicitly changed will utilize the default. This has the difficult side-effect of making the file-mask nearly transparent to the user most of the time. However, when the file-mask is wrong, users have a tendency to not understand what is happening, and get frustrated. Agar2 will have much more explicit and transparent file filters.