Distributing methods of a class across multiple files

[lh]

First, thanks for all the thoughtful replies. I am grateful.
Second, I figured I'd get a lot of judgement about how I really
shouldn't be doing this. Should have pre-empted it :-) oh well. There
is a place IMHO for filename as another structuring element to help
humans in search. Also it can be convenient to have two people who are
working on methods for one class that have different directions to
have different files (even if modern tools can handle distinct edits
on the same file by multiple folks).
Third, length. Well 5000 lines eh... I'm nowhere near that guess I can
stick with one file.
 Steven thanks especially for your thorough reply about alternatives.
Again I really appreciate the quality replies made here. very
impressed. I had not thought of the mixin approach in particular. I
was just hoping there was something like "extend class Foo" I could
put at the top of the file and then keep writing methods indented
below it. But I will think about some of these alternatives...

Humbly,
  Luke