Frames should be tested with axe-core
How to Fix the Problem
  Ensure iframe and frame elements contain the
  axe-core script.
  The after - function (optional) check is the function that gets
  called for checks that operate on a page-level basis, to process the results
  from the iframe elements.
  The pageLevel Ensures iframe and
  frame elements contain the axe-core script rule, when set to
  true, is only applied when the entire page is tested. Results from nodes on
  different frames are combined into a single result.
Why it Matters
Without the axe-core script, it is not possible for the tool to perform violation checking on multiple levels of nested iframes.
Rule Description
Frames must be tested with axe-core.
The Algorithm (in simple terms)
  The iframes property, when set to true, tells axe to run inside
  iframes. This uses both frame and iframe selectors to check for the axe-core
  script to return a "review item" result.
              