RichText samples
editor api
set selection

Getting selection. Check documentation: getSelection() method

{
	"left": {
		"blockIndex": 0,
		"textIndex": 0,
		"offset": 0
	},
	"right": {
		"blockIndex": 0,
		"textIndex": 0,
		"offset": 11
	},
	"range": true
}