Error Detection Creates False Positives if Non-US Keyboard Characters Used

In our class today a student's chromebook was, for some reason, set to use the international keyboard setting.

As a result she got an error nag about needing to use "s for her href attribute because the double-quotes were typed with international characters. The tag was visibly correct. Switching the chromebook to US Keyboard setting fixed the issue with visibly different " characters in the IDE.

Valid: <img src="//placekitten.com/100/100">
Not valid (US international keyboard): <img src=¨//placekitten.com/100/100¨>

The W3C validator gives the following error for on that character:

Line 2, Column 18: an attribute value must be a literal unless it contains only name characters
<img src=¨//placekitten.com/100/100¨>
✉
You have used a character that is not considered a "name character" in an attribute value. Which characters are considered "name characters" varies between the different document types, but a good rule of thumb is that unless the value contains only lower or upper case letters in the range a-z you must put quotation marks around the value. In fact, unless you have extreme file size requirements it is a very very good idea to always put quote marks around your attribute values. It is never wrong to do so, and very often it is absolutely necessary.

https://github.com/popcodeorg/popcode/issues/179

No source file or test is named. Reproduce the reported snippets in the editor and trace the error-detection path for international-keyboard quote characters, using issue #179 as context; done means valid-looking input no longer produces a false positive while genuinely invalid markup is still reported.