There are several questions here on how to use different syntax highlighting within heredocs, but I want to just disable it. I can expand upon any answers I get here for other syntaxes within other filetypes.
I want to disable syntax highlighting in heredocs with these matches at the start:
cat << EOF
cat <<-EOF
I have come up with this, but obviously it doesn't work:
# after/syntax/sh.vim
syntax region hereDocText matchgroup=Statement start=+<<[-\s]*EOF end=+^EOF contains=NONE