The MIME detector for a HTML file contains an additional byte in the mask. While it doesn't hurt, it is not used in the byte matching code (since it is zipped with the `pattern` iterator). I'm not clear how to test this within the `servo` code. The fix doesn't change any externally visible behavior. A test to validate the `ByteMatcher` structures would require the private ByteMatcher structures to be visible to the test. I could use a sub-module, as described at https://doc.rust-lang.org/book/testing.html#the-tests-module but this pattern doesn't appear anywhere else in the `servo` code. Source-Repo: https://github.com/servo/servo Source-Revision: 32c97b6c8d69a284a0f5a30bd68c9b8a8d00b204