Simple array access
-----
<?php

$a['b'];
$a['b']['c'];
$a[] = $b;
$a{'b'};
${$a}['b'];
-----
array(
    0: Stmt_Expression(
        expr: Expr_ArrayDimFetch(
            var: Expr_Variable(
                name: a
            )
            dim: Scalar_String(
                value: b
            )
        )
    )
    1: Stmt_Expression(
        expr: Expr_ArrayDimFetch(
            var: Expr_ArrayDimFetch(
                var: Expr_Variable(
                    name: a
                )
                dim: Scalar_String(
                    value: b
                )
            )
            dim: Scalar_String(
                value: c
            )
        )
    )
    2: Stmt_Expression(
        expr: Expr_Assign(
            var: Expr_ArrayDimFetch(
                var: Expr_Variable(
                    name: a
                )
                dim: null
            )
            expr: Expr_Variable(
                name: b
            )
        )
    )
    3: Stmt_Expression(
        expr: Expr_ArrayDimFetch(
            var: Expr_Variable(
                name: a
            )
            dim: Scalar_String(
                value: b
            )
        )
    )
    4: Stmt_Expression(
        expr: Expr_ArrayDimFetch(
            var: Expr_Variable(
                name: Expr_Variable(
                    name: a
                )
            )
            dim: Scalar_String(
                value: b
            )
        )
    )
)