Please add comments to isearch.el

[Eli Zaretskii <eliz@gnu.org>]

Would someone "in the know" please add commentary to isearch.el to
explain how the various options are passed to the commands defined
there and affect or not affect them?

The isearch.el commands are implemented using complex multi-layered
system of functions and macros that make it very hard to figure out,
just by looking at the code, which options affect what commands and in
what ways.  About the only way to find that out is by trying each
command, which is very inefficient.  I think it will help make this
file much more maintainable if commentary were added there explaining
how all of this works.  Thanks in advance.