What is the need for flag 'LYS_MAND_FALSE' to exist

[lyzliyuzhi91]

libyang/src/tree_schema.h

Line 897 in 25ede02

#define LYS_MAND_FALSE 0x40 /**< mandatory false; applicable only to ::lysp_node_choice/::lysc_node_choice,

I find nowhere to use the flag 'LYS_MAND_FALSE' in the master branch.
But in libyang1, it will be used to print yang/yin.

[michalvasko]

It is only hidden by the use of LYS_MAND_MASK.