TextAffinity 继承自： Enum

Defines the permissions which can be checked and requested.

枚举值

名称	类型	默认值	说明
UPSTREAM	—	'upstream'	The position has affinity for the downstream side of the text position, i.e. in the direction of the end of the string.
DOWNSTREAM	—	'downstream'	The position has affinity for the upstream side of the text position, i.e. in the direction of the beginning of the string.