Software licenses normally grant rights and, in turn, impose obligations. The Open Source license obligations checklists project aims to provide complete lists of license obligations that, if fulfilled without exception, very probably lead to license compliance. Rights, however, are not listed, since one of the prerequisites of entering a particular license into the project is that this license grants the elementary unrestricted, unlimited, royalty-free and non-discriminatory rights of an Open Source license such as to i) use, ii) analyze, iii) modify and iv) convey original or modified versions of the software.
The English language provides a number of direct and indirect ways to impose an obligation:
1. "YOU MUST do something" is evident.
2. "YOU MUST NOT do something" is evident.
3. "YOU MAY NOT do something" is equivalent to "YOU MUST NOT do something" and also is evident.
4. "YOU MAY ..." followed by an at first glance positive, but nevertheless somewhat restrictive statement is less evident. However, it still may contain an obligation.
	a) "YOU MAY only do something" is equivalent to "YOU MUST NOT do anything else than something".
	b) "YOU MAY do less than something" is equivalent to "YOU MUST NOT do same or more than something".
	c) "YOU MAY do up to a threshold" is equivalent to "YOU MUST NOT do more than the threshold".
5. "YOU SHOULD do something" is a recommendation, not an obligation.
6. "YOU SHOULD NOT do something" is a prohibition, not a recommendation.