opcodes like OP_VERIFY can also cause script to fail

[jdlcdl]

referencing

opcodeexplained.com/script/script.md

Line 17 in ecc3535

- If the final result left on the stack is "false".

Suggesting :

 - If the opcode functions to validate a condition and quickly terminate when that condition is not valid (ie: OP_VERIFY).
 - if OP_ENDIF is reached without a previous opening OP_IF, OP_NOTIF, or OP_ELSE.

and then as the last two in this list:

 - if at the end of the script, a conditional segment was not closed by OP_ENDIF.
 - If after the script concludes, the top of the stack is "false" (empty or zero -- regardless of additional items below).