Disabling Non-Ascii Identifier Warning for Markdown Documents

[vsch]

This is done by creating a scope for non-markdown documents and setting the inspection scope to that while disabling it for "Everywhere else".

Topic covered by https://github.com/Yaojian in https://github.com/vsch/idea-multimarkdown/issues/498#issuecomment-401528894

Duplicated here for posterity:

To suppress it only in markdown:

Step 1: Create a scope which contains all non-markdown files

Step 2: Apply the inspection for non-markdown files only

[vsch]

You will also need to add inspection which checks for mixed language character set use in identifiers if you have such in link addresses/header text/etc.