Suppress warnings for ```text code blocks

config.toml

@@ -11,6 +11,7 @@ highlight_code = true
 highlight_theme = "boron"
 bottom_footnotes = true
 insert_anchor_links = "left"
+extra_syntaxes_and_themes = ["syntaxes"]
 
 [extra]
 # Put all your custom variables here

syntaxes/custom_plain_text.sublime-syntax

@@ -0,0 +1,14 @@
+%YAML 1.2
+---
+name: Plain Text
+file_extensions: [text]
+scope: text.plain
+
+# This custom syntax for plain text only exists so we can match against ```text
+# code blocks, which are common in rustdoc. By default, only ```txt is supported
+# by Zola. Without this file, `zola build` would print spurious warnings.
+
+contexts:
+  main:
+    - match: whatever
+      scope: text.plain