csv2json.md

@@ -160,6 +160,17 @@ Given this mask, we need to apply FilterByMask to produce two streamsets:
    1.  `FilteredBasisBits` is produced by filtering the eight basis bit streams.
    2.  `FilteredMarks` is produced by filtering two streams produced from parsing: (a) the positions of starts of each record, (b) the positions of the starts of each field, and (c) the positions of any characters that need to be escaped with `\` in the JSON output (escaped_quotes and embedded newlines).
 
+Filtering reduces the length of the stream.   For example, for our example above, filtering
+the field starts yields the following.
+```
+Data stream:     "Free speech",limitation,"Never yell ""Fire!"" in a crowded theatre."
+CSV_data_mask    .11111111111..1111111111..11111111111.111111.11111111111111111111111.
+Field_starts     .1............1...........1..........................................
+Filtered_starts  1..........1.........1.......................................
+```
+
+
+
 ### Expansion of Compressed Input
 
 In this phase, `ExpandedBasisBits` is computed by expansion from `FilteredBasisBits` by insertion of zero bits at marked points.   The number of zero bits to insert is based on the template string to be inserted.