Is there a difference between `syntax on` and `syntax enable` in vimscript?

Question

In my .vimrc file I use:

syntax on

Today, I was perusing through some .vimrc files from other developers and i\'ve notice a few using:

Answer 1

What Vim Claims

For syntax on vs syntax enable, the help files claim:

The ":syntax enable" command will keep your current color settings.  This
allows using ":highlight" commands to set your preferred colors before or
after using this command.  If you want Vim to overrule your settings with the
defaults, use: >
    :syntax on

I Can't Verify These Claims

The behavior I see in Vim does not appear to match the above help statement.

After testing locally with some empty .vimrcs and experimenting with on, enable, and placement of highlight commands, I can't figure out what Vim is actually doing (I tested with highlight ColorColumn guibg=#331111 and set colorcolumn=80). Highlighting is sometimes overwritten and sometimes not.

Only Let Vim Set Syntax Once

I no longer trust Vim, so I only let syntax get set once, ever. Here's what I have in my .vimrc:

if !exists("g:syntax_on")
    syntax enable
endif

I use enable because of the above claim that it won't overwrite your settings, however it doesn't seem to make any difference when starting Vim.

More details

You can see that h g:syntax_on shows that on and enable source the same file:

Details:
The ":syntax" commands are implemented by sourcing a file.  To see exactly how
this works, look in the file:
    command     file ~
    :syntax enable  $VIMRUNTIME/syntax/syntax.vim
    :syntax on      $VIMRUNTIME/syntax/syntax.vim

If you're curious, g:syntax_on gets set in $VIMRUNTIME/syntax/synload.vim

Also running Vim with no plugins/settings vim -u NONE does NOT load any of the syntax files.