fix: Cover include macro

Author: epage

text/3503-frontmatter.md

@@ -79,14 +79,17 @@ an info-string is allowed after the opening `---` for use by the command interpr
 # Reference-level explanation
 [reference-level-explanation]: #reference-level-explanation
 
-When parsing Rust code, after stripping the shebang (`#!`), rustc will strip the frontmatter:
+When parsing Rust source, after stripping the shebang (`#!`), rustc will strip the frontmatter:
 - May include 0+ blank lines (whitespace + newline)
 - Opens with 3+ dashes followed by 0+ whitespace, an optional identifier, 0+ whitespace, and a newline
   - The variable number of dashes is an escaping mechanism in case `---` shows up in the content
 - All content is ignored by `rustc` until the same number of dashes is found at the start of a line.
   The line must terminate by 0+ whitespace and then a newline.
 - Unlike commonmark, it is an error to not close the frontmatter seeing to detect problems earlier in the process seeing as the primary content is what comes after the frontmatter
 
+This applies anywhere shebang stripping is performed.
+For example, if [`include!`](https://doc.rust-lang.org/std/macro.include.html) strips shebangs, then it will also frontmatter.
+
 As cargo will be the first step in the process to parse this,
 the responsibility for high quality error messages will largely fall on cargo.