[PATCH v2 6/9] doc: interpret-trailers: explain key format

[kristofferhaugsbakk@fastmail.com]

From: Kristoffer Haugsbakk <code@khaugsbakk.name>

A trailer key must consist of ASCII alphanumeric characters and
hyphens *only*. Let’s document it explicitly instead of relying on
readers being conservative and only basing their trailer keys on the
documentation examples.[1]

The previous commit provided us with an appropriate paragraph to
describe the key format.

† 1: Technically they would then miss out on using digits in them since
     all of the example keys just use letters and hyphens

Reported-by: Brendan Jackman <jackmanb@google.com>
Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
---

Notes (series):
    v2:
    • Remove the “paint by numbers” reference after review (unclear)
    • Add apropos footnote
    • Tweak the paragraph about how we now have a context to describe
      this format
    v1: [had a note about code spelunking (isalnum(3))]

 Documentation/git-interpret-trailers.adoc | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Documentation/git-interpret-trailers.adoc b/Documentation/git-interpret-trailers.adoc
index bcd79b19bd7..c35fa9c688d 100644
--- a/Documentation/git-interpret-trailers.adoc
+++ b/Documentation/git-interpret-trailers.adoc
@@ -18,7 +18,8 @@ Add or parse trailers metadata at the end of the otherwise
 free-form part of a commit message, or any other kind of text.
 
 A _trailer_ in its simplest form is a key-value pair with a colon as a
-separator. A _trailer block_ consists of one or more trailers. The
+separator. The _key_ consists of ASCII alphanumeric characters and
+hyphens (`-`). A _trailer block_ consists of one or more trailers. The
 trailer block needs to be preceded by a blank line, where a _blank line_
 is either an empty or a whitespace-only line. For example, in the
 following commit message
-- 
2.53.0.32.gf6228eaf9cc