Update chapters/arrays.tex

Co-authored-by: Henrik Tidefelt <henrikt@wolfram.com>

chapters/arrays.tex

@@ -948,7 +948,7 @@ \section{Indexing}\label{array-indexing}\label{indexing}
 If the number of index arguments is smaller than the number of dimensions of the array, the trailing indices will use `\lstinline!:!'.
 
 It is possible to index a general expression by enclosing it in parenthesis.
-Note that the grammar is left factored and allows indexing of \lstinline[language=grammar]!output-expression-list!, but only indexing of an expression is syntactically valid.
+Note that while the subscripts are applied to a \lstinline[language=grammar]!output-expression-list! in the grammar, it is only semantically valid when the \lstinline[language=grammar]!output-expression-list! represents an expression.
 
 It is also possible to use the array access operator to assign to element/elements of an array in algorithm sections.
 This is called an \firstuse[assignment statement!indexed]{indexed assignment statement}.