To manually test this, ensure that typing or attempting to delete text via the Delete key does not change the DOM.

initially:
| "<#selection-caret>def"

after attempting to type (typing is allowed):
| "abc<#selection-caret>def"

after attempting to type (typing is prohibited):
| "abc<#selection-caret>def"

after attempting to delete (deleting is prohibited):
| "abc<#selection-caret>def"

after attempting to delete (deleting is allowed):
| "a<#selection-caret>ef"