flex and initials with completion-styles

Question

I am using completion-styles and cannot decipher the difference between flex and initials.

Answer 1

initials matches "acronyms and initialisms", e.g., can complete "M-x lch" to list-command-history and "C-x C-f ~/sew" can match "~/src/emacs/work".

flex will match an in-order subset of characters. When completing "foo" the glob "*f*o*o*" is used, so that "foo" can complete to "frodo".

You can read more about these and other options (like basic and substring) from the docstring for completion-styles-alist.

Orderless and Fussy are third-party packages to provide additional completion styles.