correct 'value' missing data

ch02.adoc

@@ -430,8 +430,8 @@ See <<example-L.1>> and <<example-L.6>>.
 When the data values within a fragment are all the same, for each fragment, the `value` fragment array variable allows each fragment to be represented explicitly by its unique data value, rather than by reference to a fragment dataset.
 The `value` fragment array variable dimensions correspond to, and have the same sizes as, the fragment array dimensions in the same order as they appear in the conceptual fragment array.
 The `value` fragment array variable may have any data type, and contains each fragment's unique value.
-A fragment that contains wholly missing data is specified by any missing value indicated by the aggregation variable.
-See <<example-L.7>>, which uses an aggregation ancillary variable to make fragment dataset attributes available to an aggregation data variable.
+A fragment that contains wholly missing data is specified by any missing value indicated by the `value` fragment array variable.
+See <<example-L.7>>, which uses an aggregation ancillary variable to make fragment dataset global attributes available to an aggregation data variable.
 
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