diff --git a/doorstop/core/document.py b/doorstop/core/document.py
index 939d90cbb..773a90ed0 100644
--- a/doorstop/core/document.py
+++ b/doorstop/core/document.py
@@ -186,11 +186,14 @@ def load(self, reload=False):
                     self._data[key] = value.strip()
                 elif key == "digits":
                     self._data[key] = int(value)  # type: ignore
+                elif key == "mapped_to":
+                    self._data[key] = value.strip()
                 else:
-                    msg = "unexpected document setting '{}' in: {}".format(
-                        key, self.config
+                    log.debug(
+                        "custom document attribute found:  {} = {}".format(key, value)
                     )
-                    raise DoorstopError(msg)
+                    # custom attribute
+                    self._data[key] = value
             except (AttributeError, TypeError, ValueError):
                 msg = "invalid value for '{}' in: {}".format(key, self.config)
                 raise DoorstopError(msg)
@@ -437,6 +440,10 @@ def index(self):
         log.info("deleting {} index...".format(self))
         common.delete(self.index)
 
+    def attribute(self, attrib):
+        """Get the item's custom attribute."""
+        return self._data.get(attrib)
+
     # actions ################################################################
 
     # decorators are applied to methods in the associated classes
diff --git a/doorstop/core/item.py b/doorstop/core/item.py
index 9797b8e9e..18df58ed3 100644
--- a/doorstop/core/item.py
+++ b/doorstop/core/item.py
@@ -728,10 +728,18 @@ def find_child_items_and_documents(self, document=None, tree=None, find_all=True
         tree = tree or self.tree
         if not document or not tree:
             return child_items, child_documents
+
+        # get list of mapped documents
+        mapped_document_prefixes = document.attribute("mapped_to") if document else []
+        if not mapped_document_prefixes:
+            mapped_document_prefixes = []
+
         # Find child objects
         log.debug("finding item {}'s child objects...".format(self))
         for document2 in tree:
-            if document2.parent == document.prefix:
+            if (document2.parent == document.prefix) or (
+                document2.prefix in mapped_document_prefixes
+            ):
                 child_documents.append(document2)
                 # Search for child items unless we only need to find one
                 if not child_items or find_all:
diff --git a/doorstop/core/tests/__init__.py b/doorstop/core/tests/__init__.py
index c51863b3f..ad7005669 100644
--- a/doorstop/core/tests/__init__.py
+++ b/doorstop/core/tests/__init__.py
@@ -4,7 +4,7 @@
 
 import logging
 import os
-from typing import List
+from typing import Dict, List
 from unittest.mock import MagicMock, Mock, patch
 
 from doorstop.core.base import BaseFileObject
@@ -95,6 +95,7 @@ def __init__(self):
         self.prefix = "RQ"
         self._items: List[Item] = []
         self.extended_reviewed: List[str] = []
+        self._data: Dict[str, str] = {}
 
     def __iter__(self):
         yield from self._items
@@ -102,6 +103,12 @@ def __iter__(self):
     def set_items(self, items):
         self._items = items
 
+    def set_data(self, data):
+        self._data = data
+
+    def attribute(self, name):
+        return self._data.get(name)
+
 
 class MockDocumentSkip(MockDocument):  # pylint: disable=W0223,R0902
     """Mock Document class that is always skipped in tree placement."""
diff --git a/doorstop/core/tests/test_document.py b/doorstop/core/tests/test_document.py
index ebc3883d8..9725eaad6 100644
--- a/doorstop/core/tests/test_document.py
+++ b/doorstop/core/tests/test_document.py
@@ -159,8 +159,8 @@ def test_load_invalid(self):
     def test_load_unknown(self):
         """Verify loading a document config with an unknown key fails."""
         self.document._file = YAML_UNKNOWN
-        msg = "^unexpected document setting 'John' in: .*\\.doorstop.yml$"
-        self.assertRaisesRegex(DoorstopError, msg, self.document.load)
+        self.document.load()
+        self.assertEqual("Doe", self.document.attribute("John"))
 
     def test_load_unknown_attributes(self):
         """Verify loading a document config with unknown attributes fails."""
diff --git a/doorstop/core/tree.py b/doorstop/core/tree.py
index 156f75b1b..7112a3872 100644
--- a/doorstop/core/tree.py
+++ b/doorstop/core/tree.py
@@ -627,9 +627,16 @@ def _draw_line(self):
     def _draw_lines(self, encoding, html_links=False):
         """Generate lines of the tree structure."""
         # Build parent prefix string (`getattr` to enable mock testing)
-        prefix = getattr(self.document, "prefix", "") or str(self.document)
+        prefix_link = prefix = getattr(self.document, "prefix", "") or str(
+            self.document
+        )
+
+        attribute_fn = getattr(self.document, "attribute", None)
+        mapped = attribute_fn("mapped_to") if callable(attribute_fn) else None
+
+        prefix += " (" + ",".join(mapped) + ")" if mapped else ""
         if html_links:
-            prefix = '<a href="documents/{0}">{0}</a>'.format(prefix)
+            prefix = '<a href="documents/{0}">{1}</a>'.format(prefix_link, prefix)
         yield prefix
         # Build child prefix strings
         for count, child in enumerate(self.children, start=1):
diff --git a/doorstop/core/validators/item_validator.py b/doorstop/core/validators/item_validator.py
index 94abfbc48..c240a88a1 100644
--- a/doorstop/core/validators/item_validator.py
+++ b/doorstop/core/validators/item_validator.py
@@ -198,7 +198,13 @@ def _get_issues_both(self, item, document, tree, skip):
 
         # Verify an item is being linked to (child links)
         if settings.CHECK_CHILD_LINKS and item.normative:
-            find_all = settings.CHECK_CHILD_LINKS_STRICT or False
+
+            mapped_document_prefixes = document.attribute("mapped_to")
+            if not mapped_document_prefixes:
+                mapped_document_prefixes = []
+
+            find_all = settings.CHECK_CHILD_LINKS_STRICT or mapped_document_prefixes
+
             items, documents = item.find_child_items_and_documents(
                 document=document, tree=tree, find_all=find_all
             )
@@ -209,13 +215,64 @@ def _get_issues_both(self, item, document, tree, skip):
                         msg = "skipping issues against document %s..."
                         log.debug(msg, child_document)
                         continue
-                    msg = "no links from child document: {}".format(child_document)
+
+                    if child_document.prefix in mapped_document_prefixes:
+                        msg = "no links at all, missing mapped document: {}".format(
+                            child_document
+                        )
+                    else:
+                        msg = "no links at all, missing child document: {}".format(
+                            child_document
+                        )
                     yield DoorstopWarning(msg)
-            elif settings.CHECK_CHILD_LINKS_STRICT:
+
+            # here items are found but no strict checking is enabled
+            # only check "mapped_to" as mandatory links
+            else:
                 prefix = [item.document.prefix for item in items]
-                for child in document.children:
+
+                found = False
+                not_found_list = []
+
+                # check if at least on of the normal children exist
+                for child_document in documents:
+                    if child_document.prefix in skip:
+                        msg = "skipping issues against document %s..."
+                        log.debug(msg, child_document)
+                        continue
+
+                    # handle mapped documents later
+                    if child_document.prefix in mapped_document_prefixes:
+                        continue
+
+                    if child_document.prefix in prefix:
+                        # found at least one link from child document
+                        found = True
+                    else:
+                        not_found_list.append(child_document.prefix)
+
+                # not found anything but not strict: accept a link from any child document
+                if not found and not settings.CHECK_CHILD_LINKS_STRICT:
+                    for d in not_found_list:
+                        msg = "links found, missing at lest one document: {}".format(d)
+                        yield DoorstopWarning(msg)
+
+                if settings.CHECK_CHILD_LINKS_STRICT:
+                    # if strict check: report any document with no child links
+                    for d in not_found_list:
+                        msg = "no links from document: {}".format(d)
+                        yield DoorstopWarning(msg)
+
+                # handle mapped documents: they are treated like "strict"
+                for child in mapped_document_prefixes:
+                    if child in skip:
+                        msg = "skipping issues against mapped document %s..."
+                        log.debug(msg, child)
+                        continue
+
                     if child in skip:
                         continue
+
                     if child not in prefix:
-                        msg = "no links from document: {}".format(child)
+                        msg = "no links from mapped document: {}".format(child)
                         yield DoorstopWarning(msg)