diff --git a/README.md b/README.md
index 2f51d3e..8377e16 100644
--- a/README.md
+++ b/README.md
@@ -175,11 +175,16 @@ This configuration is a `.json` file in the following format.
         "flags": "gu"
       },
       {
-        "pattern": "(.) (.+)",
-        "target": "$1",
-        "on_property": "title"
+        "pattern": "\\[Issue\\]",
+        "on_property": "title",
+        "method": "match"
       }
     ],
+    "duplicate_filter": {
+      "pattern": "\\[ABC-....\\]",
+      "on_property": "title",
+      "method": "match"
+    },
     "transformers": [
       {
         "pattern": "[\\-\\*] (\\[(...|TEST|CI|SKIP)\\])( )?(.+?)\n(.+?[\\-\\*] )(.+)",
@@ -296,12 +301,13 @@ Table of descriptions for the `configuration.json` options to configure the resu
 | template                    | Specifies the global template to pick for creating the changelog. See [Template placeholders](#template-placeholders) for possible values                                                                                          |
 | pr_template                 | Defines the per pull request template. See [PR Template placeholders](#pr-template-placeholders) for possible values                                                                                                               |
 | empty_template              | Template to pick if no changes are detected. See [Template placeholders](#template-placeholders) for possible values                                                                                                               |
-| label_extractor             | An array of `transform` specifications, offering a flexible API to extract additinal labels from a PR (Default: `body`, Default in commit mode: `commit message`).                                                                 |
+| label_extractor             | An array of `Extractor` specifications, offering a flexible API to extract additinal labels from a PR (Default: `body`, Default in commit mode: `commit message`).                                                                 |
 | label_extractor.pattern     | A `regex` pattern, extracting values of the change message.                                                                                                                                                                        |
 | label_extractor.target      | The result pattern. The result text will be used as label. If empty, no label is created. (Unused for `match` method)                                                                                                              |
 | label_extractor.on_property | The property to retrieve the text from. This is optional. Defaults to: `body`. Alternative values: `title`, `author`, `milestone`.                                                                                                 |
 | label_extractor.method      | The extraction method used. Defaults to: `replace`. Alternative value: `match`. The method specified references the JavaScript String method.                                                                                      |
 | label_extractor.flags       | Defines the regex flags specified for the pattern. Default: `gu`                                                                                                                                                                   |
+| duplicate_filter            | Defines the `Extractor` to use for retrieving the identifier for a PR. In case of duplicates will keep the last matching pull request (depends on `sort`). See `label_extractor` for details on `Extractor` properties.            |
 | transformers                | An array of `transform` specifications, offering a flexible API to modify the text per pull request. This is applied on the change text created with `pr_template`. `transformers` are executed per change, in the order specified |
 | transformer.pattern         | A `regex` pattern, extracting values of the change message.                                                                                                                                                                        |
 | transformer.target          | The result pattern, the regex groups will be filled into. Allows for full transformation of a pull request message. Including potentially specified texts                                                                          |