The Force Place capability bypasses normal placement restrictions.
- Blocks which normally need to be attached to solid blocks can be placed in mid air
- Blocks can be placed inside entities (including yourself)
- Plant blocks no longer need to be placed on farmland
- Blocks can be placed regardless of light level
- And much more!
Force Place is best used in combination with No Updates in order to ensure illegally placed blocks don't break when updated. You may also need to disable random updates with /gamerule randomTickSpeed 0