Start in "code" mode exclusively

[stasm]

@markusicu wrote in #230 (comment):

First, to a human, there is no clear mental model for how to start reading and writing a message. A message can just be plain text (yeah!), or text in square brackets, or "code". I see how you get that to work in the EBNF, but it's confusing.

I have always liked simple messages to be simple, with no surrounding syntax. However, that should include placeholders, requiring enclosing-delimiter syntax only when there are placeholders is weird, and allowing simple text both with and without delimiters is also weird.

Starting in "text" mode also has problems discussed here (uncertainty about trimming spaces), and we have problems with MF1 (ICU MessageFormat) where we don't want people to write literal text outside of a select-type placeholder.

So while it pains me to say this, bite the bullet, start in "code" mode, and always surround translatable text with delimiters.

[stasm]

There's one advantage of starting in the "code" mode exclusively which I didn't consider before. It came up when @mihnita was talking about transition paths from other formats to MF2, or more generally, about scenarios in which vendors work with messages stored in multiple different formats.

When we see something like hello = Hello! in a resource file, it's not immediately clear that we're looking at an MF2 message. It could be any sort of templating language, admittedly. When we add a placeholder (hello = Hello, {$name}!), it becomes possible to narrow down the set of templating languages, but it still requires remembering exactly what the syntax of the placeholder is. Compare the following messages — which one is MF2?

hello = Hello, %(name)s!
hello = Hello, {{name}}!
hello = Hello, {$name}!

The requirement to wrap all translatable text in delimiters is a chance to create a "signature" of the MF2 syntax, making it instantly recognizable. For example:

hello = Hello, %(name)s!
hello = Hello, {{name}}!
hello = [Hello, {$name}!]

(See #255 for the discussion about which delimiters to pick.)

[echeran]

+1 to starting in code mode (even though the consequence is that we need to have delimiters for simple message patterns, too).

Also, more than what the actual delimiter is (#255), I think the important attribute to me is that if we always have a delimiter for a simple message pattern, then we should use that same delimiter to delimit all of the patterns in the selection message.

[eemeli]

Closed by #287.