Found this, but need help to decipher the formula

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* returns the characters between the 3rd and 4th underscores (_):*

With Text in Cell A1: COMP_PROG_v1_ABCD_01
This formula in Cell B1 returns the characters between the 3rd and 4th underscores (_): B1: =TRIM(LEFT(SUBSTITUTE(MID(A1,FIND("|",SUBSTITUTE(A 1,"_","|",3))+1,LEN(A1)),"_",REPT(" ",LEN(A1))),LEN(A1)))
In the above example, the formula returns: ABCD
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Thanks.