It is not in the glossary. Since these sentences are in the guidelines, perhaps we should avoid that word in the rationale - since they are not P1 checkpoints. Guideline 1 last sentence is not a sentence. For example, on a windows machine say I use the Microsoft Foundation Classes and implement Active Accessibility - I assume these are the higher level APIs. What about Java - it is device independent and up to the virtual machine to use the standard devices correctly.
Several checkpoints refer to using operating system conventions.
In that case it is up to the virtual machine to use the system conventions. Also, section 3.2. Also, what about user agents that are intended to run, with minimal modification, on a variety of operating systems. This is supposedly Mozilla's strategy. 2.1 and 2.3 seem very redundant or that 2.3 is a technique of 2.1.