Fixes #1913

[georgeraraujo]

• [X] I provide my work under the project license.
• [X] I grant such license of my work as is required for the purposes of future print editions to Ben Straub and Scott Chacon.

Changes

• Replace + that should output a literal plus but is interpreted as an inline passthrough with a {plus} attribute reference

Context

Fixes #1913

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EPUB, broken:

EPUB, fixed:

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PDF, broken:

PDF, fixed: