Document (or change) the severity column in accessibility audit procedure

[sandbergja]

The accessibility audit spreadsheet has a column named Severity, with the following options:

• "Critical"
• "High"
• "Medium"
• "Low"

I took these levels from the OIT key sites audit. @christinach's audit of the catalog included the Deque impact levels instead. We don't yet have any procedures for determining how severe an issue is.

We should:

• Decide what scale we want to use for the severity column. The deque one? The OIT one? Or something different?
• In the accessibility audit procedure, add information about the different severity levels, either in our handbook or linking out to another resource. For what it's worth, Deque has good descriptions of their severity levels, and this Ontario Ecampus page seemed like a good description of the OIT scale.