Function validate_room_base 

pub fn validate_room_base(
    event_type: &str,
    types: &[TypeDef],
    base_seq: u64,
    base_hash: &str,
    anchor_hash: Option<&str>,
    head_seq: u64,
) -> Result<()>

Section 5.1 base check for a room write based on base_seq / base_hash. anchor_hash is the hash of the accepted record at base_seq in the same room (None when there is none) and head_seq is the current room head. Every base must name an accepted record (base_record_mismatch); message and control writes must also be based at or after the head (room_head_mismatch).