The [] binary operator performs a subscripting (or indexing) operation between the operand to the left of the brackets and the operand enclosed within the brackets. This is a simple additive operation of BYTE granularity; the arithmetic performed is not influenced by the Operand Size of either operand.
The syntax for this operator describes a binary operation between the left hand expression and the bracketed expression. The bracketed expression is also subject to the same operations performed during the processing of a standalone Indirected-Expression as described in the section on Primary-Expressions.