I have problem understanding bos/eos

> Matches at the beginning/end of string without consuming any characters (a zero-width assertion).

OK So far so good.

> If the search was initiated with start/end parameters, these are considered the end points, rather than the full string.

What are "these", bos/eos or start/end parameters? If "these" are
bos/eos what does "considered the end points" really mean? bos/eos
match start/end parameters respectively?

Or does it mean start/end parameters are irrelevant and bos/eos still
match the true beginning/end of the string?
--
Duy