Question: Any reason to use non-standard placeholder formatting?

[kou1okada]

Question: Any reason to use non-standard placeholder formatting?

[kou1okada]

I don't think so.
It is not non-standard style, but it's traditional UNIX style.
For examples, we can see it in manpages of UNIX like system as grep, ls, sort and many other commands as below:

grep [OPTIONS] PATTERN [FILE...]

Maybe the style, which you are shown, is the standard one at Microsoft.
And we can see it in reference manuals of Microsoft at cmd, copy, dir and many other commands.
But in a recent case, git adopts a similar style which you showed.
And, apt-get seems to adopt an intermediate style.

Hmm,,,
O.K.
I'll reconsider about placeholders style.

Currently, I feel the following rules to be reasonable.

Style	Description
something	Fixed string
<something>	Placeholder
[something]	Optional
{foo|bar|...}	Choose one of them
...	Previous element can repeatable