[DOCS] Reformat length token filter docs (#49805)

* Adds a title abbreviation
* Updates the description and adds a Lucene link
* Reformats the parameters section
* Adds analyze, custom analyzer, and custom filter snippets

Relates to #44726.

docs/reference/analysis/tokenfilters/length-tokenfilter.asciidoc

@@ -1,16 +1,170 @@
 [[analysis-length-tokenfilter]]
-=== Length Token Filter
+=== Length token filter
+++++
+<titleabbrev>Length</titleabbrev>
+++++
 
-A token filter of type `length` that removes words that are too long or
-too short for the stream.
+Removes tokens shorter or longer than specified character lengths.
+For example, you can use the `length` filter to exclude tokens shorter than 2
+characters and tokens longer than 5 characters.
 
-The following are settings that can be set for a `length` token filter
-type:
+This filter uses Lucene's
+https://lucene.apache.org/core/{lucene_version_path}/analyzers-common/org/apache/lucene/analysis/miscellaneous/LengthFilter.html[LengthFilter].
 
-[cols="<,<",options="header",]
-|===========================================================
-|Setting |Description
-|`min` |The minimum number. Defaults to `0`.
-|`max` |The maximum number. Defaults to `Integer.MAX_VALUE`, which is `2^31-1` or 2147483647.
-|===========================================================
+[TIP]
+====
+The `length` filter removes entire tokens. If you'd prefer to shorten tokens to
+a specific length, use the <<analysis-truncate-tokenfilter,`truncate`>> filter.
+====
 
+[[analysis-length-tokenfilter-analyze-ex]]
+==== Example
+
+The following <<indices-analyze,analyze API>> request uses the `length`
+filter to remove tokens longer than 4 characters:
+
+[source,console]
+--------------------------------------------------
+GET _analyze
+{
+  "tokenizer": "whitespace",
+  "filter": [
+    {
+      "type": "length",
+      "min": 0,
+      "max": 4
+    }
+  ],
+  "text": "the quick brown fox jumps over the lazy dog"
+}
+--------------------------------------------------
+
+The filter produces the following tokens:
+
+[source,text]
+--------------------------------------------------
+[ the, fox, over, the, lazy, dog ]
+--------------------------------------------------
+
+/////////////////////
+[source,console-result]
+--------------------------------------------------
+{
+  "tokens": [
+    {
+      "token": "the",
+      "start_offset": 0,
+      "end_offset": 3,
+      "type": "word",
+      "position": 0
+    },
+    {
+      "token": "fox",
+      "start_offset": 16,
+      "end_offset": 19,
+      "type": "word",
+      "position": 3
+    },
+    {
+      "token": "over",
+      "start_offset": 26,
+      "end_offset": 30,
+      "type": "word",
+      "position": 5
+    },
+    {
+      "token": "the",
+      "start_offset": 31,
+      "end_offset": 34,
+      "type": "word",
+      "position": 6
+    },
+    {
+      "token": "lazy",
+      "start_offset": 35,
+      "end_offset": 39,
+      "type": "word",
+      "position": 7
+    },
+    {
+      "token": "dog",
+      "start_offset": 40,
+      "end_offset": 43,
+      "type": "word",
+      "position": 8
+    }
+  ]
+}
+--------------------------------------------------
+/////////////////////
+
+[[analysis-length-tokenfilter-analyzer-ex]]
+==== Add to an analyzer
+
+The following <<indices-create-index,create index API>> request uses the
+`length` filter to configure a new 
+<<analysis-custom-analyzer,custom analyzer>>.
+
+[source,console]
+--------------------------------------------------
+PUT length_example
+{
+  "settings": {
+    "analysis": {
+      "analyzer": {
+        "standard_length": {
+          "tokenizer": "standard",
+          "filter": [ "length" ]
+        }
+      }
+    }
+  }
+}
+--------------------------------------------------
+
+[[analysis-length-tokenfilter-configure-parms]]
+==== Configurable parameters
+
+`min`::
+(Optional, integer)
+Minimum character length of a token. Shorter tokens are excluded from the
+output. Defaults to `0`.
+
+`max`::
+(Optional, integer)
+Maximum character length of a token. Longer tokens are excluded from the output.
+Defaults to `Integer.MAX_VALUE`, which is `2^31-1` or `2147483647`.
+
+[[analysis-length-tokenfilter-customize]]
+==== Customize
+
+To customize the `length` filter, duplicate it to create the basis
+for a new custom token filter. You can modify the filter using its configurable
+parameters.
+
+For example, the following request creates a custom `length` filter that removes
+tokens shorter than 2 characters and tokens longer than 10 characters:
+
+[source,console]
+--------------------------------------------------
+PUT length_custom_example
+{
+  "settings": {
+    "analysis": {
+      "analyzer": {
+        "whitespace_length_2_to_10_char": {
+          "tokenizer": "whitespace",
+          "filter": [ "length_2_to_10_char" ]
+        }
+      },
+      "filter": {
+        "length_2_to_10_char": {
+          "type": "length",
+          "min": 2,
+          "max": 10
+        }
+      }
+    }
+  }
+}
+--------------------------------------------------