Minor Description
In .script files, the "index" value of the "foreach" tag is stored as a String, not an integer.
If you have a two-dimensional array stored in the input-symbol "matrix", the following will work fine:
${matrix[0].length}
But the following, where "matrixIndex" is the symbol used for a surrounding "foreach"-tag's "index" value, will throw an error:
${matrix[matrixIndex].length}
The error will tell you that "matrix" does not have the property: 0.
i.e. since matrixIndex is a String, it's looking for a property of the array-object named "0".
This issue doesn't arise with comparisons, such as ${matrixIndex > 0}, because OGNL knows to interpret matrixIndex as an integer. However, again, in the case of indexes to [ ], both an integer and String parameter are acceptable, so no implicit casting is done on the String.
A workaround: ${matrix[@java.lang.Integer@parseInt(matrixIndex)].length}