What is Cross-Browser testing

What should we validate in Cross-Browser testing? As far as, I have found a way on this, my understanding is as below with each category explained on its approach:

  1. Validating CSS
  2. Page Element Operations (E.g. Click, LoseFocus, Submit etc) on plain browser or without JS
  3. Images and their URLs
  4. Font sizes (from browser)
  5. Zoom behaviours by browser
  6. All Links Validation (Recursively)
  7. Text/Images and their alignment
  8. Shift text positions
  9. DATEs format validation
  10. Page design in Mobile/Portrait/Landscape View
  11. Multi-byte/Special Characters

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