The description of the 'older-kernels-compatibility' USE-flag in dev-libs/apr is vague: "Enable binary compatibility with older kernels". It fails to specify what constitutes an "older kernel", which could mean anything from "pre-2.6.30" to "pre-1.0". Reproducible: Always Steps to Reproduce:
This USE flag can mean compatibility with different versions of kernels in case of different versions of APR. In case of 1.3.8, it means kernels <2.6.28.
It probably makes sense to document it in the ebuild (e.g. as a comment) so that the information can be found somewhere if needed.