Editorial: Fix some links and other Bikeshed warnings

[inexorabletash]

• RFC2119 "may" -> "can" in several places
• Ignore a domintro var
• Fix links around permissions/permissions policy dfn/use

NOTE: Following this change there are still some RFC2119 warnings but some of them MAY merit moving to a normative section.

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[inexorabletash]

@michaelwasserman @bradtriebwasser - care to review?

[michaelwasserman]

Thank you!