Specify element count limit (#926)

Author: philloooo

index.bs

@@ -1697,6 +1697,16 @@ An {{MLOperandDescriptor}} |A| is <dfn for=MLOperandDescriptor>equal</dfn> to an
     1. Return |elementLength| * |elementSize|.
 </details>
 
+<details open algorithm>
+  <summary>
+    The <dfn for="MLOperandDescriptor">element count</dfn> of an {{MLOperandDescriptor}} |desc| is the value returned by the following steps:
+  </summary>
+    1. Let |elementCount| be 1.
+    1. [=list/For each=] |dimension| of |desc|.{{MLOperandDescriptor/shape}}:
+        1. Set |elementCount| to |elementCount| * |dimension|.
+    1. Return |elementCount|.
+</details>
+
 <p>
 A <dfn>valid dimension</dfn> is an integer greater than zero and in the range of {{long}}. Implementations may impose a smaller upper bound.
 </p>
@@ -1712,6 +1722,7 @@ Issue(391): Should 0-size dimensions be supported?
 
         Issue(456): The maximum number of operand dimensions is not defined, but native ML APIs usually have a maximum supported size.
 
+    1. If |descriptor|'s [=MLOperandDescriptor/element count=] is not a [=valid dimension=], then return false.
     1. If |descriptor|'s [=MLOperandDescriptor/byte length=] is not supported by the implementation, then return false.
     1. Return true.
 </details>