1. document api: execcommand

2. document api: execcommand: `copy` command

3. document api: execcommand: `cut` command

4. document api: execcommand: `defaultparagraphseparator` command

5. document api: execcommand: `insertbronreturn` command

6. document api: execcommand: `inserthtml` command

7. document api: execcommand: `inserthtml` command: requires `trustedhtml` instance when trusted types are enforced

8. document api: execcommand: `paste` command