add DimensionSpecs docs

docs/content/DimensionSpecs.md

@@ -0,0 +1,76 @@
+---
+layout: doc_page
+---
+
+## DimensionSpec
+
+`DimensionSpec`s define how dimension values get transformed prior to aggregation.
+
+### DefaultDimensionSpec
+
+Returns dimension values as is and optionally renames renames the dimension.
+
+```json
+{ "type" : "default", "dimension" : <dimension>, "outputName": <output_name> }
+```
+
+### ExtractionDimensionSpec
+
+Returns dimension values transformed using the given [DimExtractionFn](#toc_3)
+
+```json
+{
+  "type" : "extraction",
+  "dimension" : <dimension>,
+  "outputName" :  <output_name>,
+  "dimExtractionFn" : <dim_extraction_fn>
+}
+```
+
+## DimExtractionFn
+
+`DimExtractionFn`s define the transformation applied to each dimenion value
+
+### RegexDimExtractionFn
+
+Returns the first group matched by the given regular expression. If there is no match it returns the dimension value as is.
+
+```json
+{ "type" : "regex", "expr", <regular_expression> }
+```
+
+### PartialDimExtractionFn
+
+Returns the dimension value as is if there is a match, otherwise returns null.
+
+```json
+{ "type" : "partial", "expr", <regular_expression> }
+```
+
+### SearchQuerySpecDimExtractionFn
+
+Returns the dimension value as is if the given [SearchQuerySpec](SearchQuerySpec.html) matches, otherwise returns null.
+
+```json
+{ "type" : "searchQuery", "query" : <search_query_spec> }
+```
+
+### TimeDimExtractionFn
+
+Parses dimension values as timestamps using the given input format, and returns them formatted using the given output format. Time formats follow the [com.ibm.icu.text.SimpleDateFormat](http://icu-project.org/apiref/icu4j/com/ibm/icu/text/SimpleDateFormat.html) format
+
+```json
+{ "type" : "time", "timeFormat" : <input_format>, "resultFormat" : <output_format> }
+```
+
+### JavascriptDimExtractionFn
+
+Returns the dimension value as transformed by the given JavaScript function.
+
+Example
+
+```json
+{
+  "type" : "javascript",
+  "function" : "function(str) { return str.substr(0, 3); }"
+}

docs/content/toc.textile

@@ -36,6 +36,7 @@ h2. Querying
 ** "Aggregations":./Aggregations.html
 ** "Post Aggregations":./Post-aggregations.html
 ** "Granularities":./Granularities.html
+** "DimensionSpecs":./DimensionSpecs.html
 * Query Types
 ** "GroupByQuery":./GroupByQuery.html
 *** "OrderBy":./OrderBy.html