[DOCS] Reformat decimal digit token filter

docs/reference/analysis/tokenfilters/decimal-digit-tokenfilter.asciidoc

@@ -1,4 +1,89 @@
 [[analysis-decimal-digit-tokenfilter]]
-=== Decimal Digit Token Filter
+=== Decimal digit token filter
+++++
+<titleabbrev>Decimal digit</titleabbrev>
+++++
 
-The `decimal_digit` token filter folds unicode digits to `0-9`
+Converts all digits in the Unicode `Decimal_Number` General Category to `0-9`.
+For example, the filter changes the Bengali numeral `৩` to `3`.
+
+This filter uses Lucene's
+https://lucene.apache.org/core/{lucene_version_path}/analyzers-common/org/apache/lucene/analysiscore/DecimalDigitFilter.html[DecimalDigitFilter].
+
+[[analysis-decimal-digit-tokenfilter-analyze-ex]]
+==== Example
+
+The following <<indices-analyze,analyze API>> request uses the `decimal_digit`
+filter to convert Devanagari numerals to `0-9`:
+
+[source,console]
+--------------------------------------------------
+GET /_analyze
+{
+  "tokenizer" : "whitespace",
+  "filter" : ["decimal_digit"],
+  "text" : "१-one two-२ ३"
+}
+--------------------------------------------------
+
+The filter produces the following tokens:
+
+[source,text]
+--------------------------------------------------
+[ 1-one, two-2, 3]
+--------------------------------------------------
+
+/////////////////////
+[source,console-result]
+--------------------------------------------------
+{
+  "tokens" : [
+    {
+      "token" : "1-one",
+      "start_offset" : 0,
+      "end_offset" : 5,
+      "type" : "word",
+      "position" : 0
+    },
+    {
+      "token" : "two-2",
+      "start_offset" : 6,
+      "end_offset" : 11,
+      "type" : "word",
+      "position" : 1
+    },
+    {
+      "token" : "3",
+      "start_offset" : 12,
+      "end_offset" : 13,
+      "type" : "word",
+      "position" : 2
+    }
+  ]
+}
+--------------------------------------------------
+/////////////////////
+
+[[analysis-decimal-digit-tokenfilter-analyzer-ex]]
+==== Add to an analyzer
+
+The following <<indices-create-index,create index API>> request uses the
+`decimal_digit` filter to configure a new 
+<<analysis-custom-analyzer,custom analyzer>>.
+
+[source,console]
+--------------------------------------------------
+PUT /decimal_digit_example
+{
+    "settings" : {
+        "analysis" : {
+            "analyzer" : {
+                "whitespace_decimal_digit" : {
+                    "tokenizer" : "whitespace",
+                    "filter" : ["decimal_digit"]
+                }
+            }
+        }
+    }
+}
+--------------------------------------------------