If there is a text or node selection, this selection is deleted.

If the caret is inside an empty text node, this empty text node is deleted. If the empty text node is the sole child of its parent element, it is the parent element as a whole which is deleted.

If the caret is found at the very end of a block, this block is merged with the immediately following, similar, block (if any).

To make it simple, a block is a paragraph or a list item. However what is exactly a block must be specified as explained in Section 50.1, “Specifying splittable blocks”.

If option backwards is specified and the caret is found at the very beginning of a block, then this block is merged with the immediately preceding, similar, block (if any).

Otherwise, delete the character found after the caret. If option backwards is specified, delete the character found before the caret.