Colon-delimitation of commands in `BROWSER` is not respected

[tremby]

Projects with Storybook set up (which it seems uses better-opn) fail to start for me, unless I override BROWSER for the command. For a dozen years or more mine has been set to x-www-browser:www-browser.

I forget what prompted me to set it that way originally, and it's a bit hard to find documentation of exactly what BROWSER is supposed to be. After a bit of digging I found this Stackoverflow question which asks where the docs are, and one of the answers says

The BROWSER variable is not in the same league as EDITOR or PAGER - it is not mentioned by the standards. However, some programs may use them, like man:

man 1 man (Debian):

BROWSER
      If $BROWSER is set, its value is a colon-delimited list of  com-
      mands,  each  of  which  in  turn  is used to try to start a web
      browser for man --html.  In each command, %s is  replaced  by  a
      filename  containing  the HTML output from groff, %% is replaced
      by a single percent sign (%), and %c is replaced by a colon (:).

Right now when it's set with a colon-separated list, better-opn fails:

node:events:368
      throw er; // Unhandled 'error' event
      ^

Error: spawn x-www-browser:www-browser ENOENT
    at Process.ChildProcess._handle.onexit (node:internal/child_process:282:19)
    at onErrorNT (node:internal/child_process:477:16)
    at processTicksAndRejections (node:internal/process/task_queues:83:21)
Emitted 'error' event on ChildProcess instance at:
    at Process.ChildProcess._handle.onexit (node:internal/child_process:288:12)
    at onErrorNT (node:internal/child_process:477:16)
    at processTicksAndRejections (node:internal/process/task_queues:83:21) {
  errno: -2,
  code: 'ENOENT',
  syscall: 'spawn x-www-browser:www-browser',
  path: 'x-www-browser:www-browser',
  spawnargs: [ 'http://localhost:6006/' ]
}

because I don't have anything called x-www-browser:www-browser.

To follow the way man uses the variable better-opn would try each of the commands in turn. If that's overkill, just splitting by colon then running the first one would be an improvement.