Tweak introduction of swizzled_vec

Improve the wording in the introduction of the section on
`__swizzled_vec__` based on review comment feedback.

adoc/chapters/programming_interface.adoc

@@ -17638,15 +17638,16 @@ member function template.
 ==== The [code]#+__swizzled_vec__+# class
 
 The [code]#+__swizzled_vec__+# class is a view over a [code]#vec# object which
-reflects a swizzle operation.
+captures the effects of a swizzle operation without actually performing that
+operation.
 The tables below define the interface to this class, but in general it supports
 the same interface as [code]#vec#.
 Member functions and operators that read elements from the
-[code]#+__swizzled_vec__+# return the values of elements from the underlying
-[code]#vec# as if it had been modified by the swizzle operation.
+[code]#+__swizzled_vec__+# return elements from the underlying [code]#vec# as
+translated by the captured swizzle operation.
 Member functions and operators that modify elements of the
 [code]#+__swizzled_vec__+# modify corresponding elements of the underlying
-[code]#vec# as translated by the swizzle operation.
+[code]#vec# as translated by the captured swizzle operation.
 The following example illustrates this behavior:
 
 [source,,linenums]

adoc/code/swizzle-example.cpp

@@ -11,4 +11,6 @@ int main() {
   int i = v.swizzle<2,1>()[1];           // i has the value 6
   v.swizzle<2>() = 0;                    // v is now {5,6,0,8}
   v.swizzle<1>()++;                      // v is now {5,7,0,8}
+  v.swizzle<2,3>();                      // Has no effect because result of swizzle is
+                                         // neither read nor modified
 }