How do I search for two separate text strings in an emacs buffer SIMULTANEOUSLY?

Question

For example, I open a file called "abc.txt". Now I want to search for all occurrences of "he is" and "first" simultaneously. I want to be able to do a search forward i.e. Ctrl-s and I'll reach the next instance of either of the two search strings.

Answer 1

M-x isearch-forward-regexp he is\|first

That command can also be found on C-u C-s and C-M-s

Answer 2

Just search for a regular expression, using e.g. search-forward-regexp with an appropriate regex search string:

he is\|first