MSTP IST( MSTI0) vs MIST confusion

Hi fellas,

I am reading MSTP and i came across two terminologies IST and MIST.
IST is used to send all the BPDU related information which is all the
information regarding which VLANS mapped to which instances and to maintain
consistency check on all the switches.
Now there is a line which states " *MSTI information is attached to IST *"
What does MSTI carry and why does it use IST for that
Correct me if i am wrong in understanding the logic.

I have a confusion regarding Internal Spanning tree (IST) aka MST Instance
0 and Multiple Intances of Spanning tree(MIST). Can some point me what is
the difference between IST and MST ?

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