Question on YAML 1.2 spec Example 9.5

To the YAML 1.2 spec writers,

In the current draft's Example 9.5:

%YAML 1.2
---
% of matches: 20
...
%YAML1.2
---
# Empty
...

"% of matches: 20" seems to be a valid node, but I don't see how
that's possible. "% of matches" is acting as a plain-style mapping
key. Plain scalars cannot start with an indicator character such as %.
How, then, is this allowed? (For the record, according to Instant
YAML, PyYaml says that this is indeed invalid in YAML 1.1.)

Sincerely,
Joshua Choi

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