diff --git a/src/main/resources/org/eolang/lints/refs/base-must-be-merged.xsl b/src/main/resources/org/eolang/lints/refs/base-must-be-merged.xsl
new file mode 100644
index 000000000..684a99102
--- /dev/null
+++ b/src/main/resources/org/eolang/lints/refs/base-must-be-merged.xsl
@@ -0,0 +1,38 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  ~ SPDX-FileCopyrightText: Copyright (c) 2016-2025 Objectionary.com
+  ~ SPDX-License-Identifier: MIT
+  -->
+<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:eo="https://www.eolang.org" id="base-must-be-merged" version="2.0">
+  <xsl:import href="/org/eolang/parser/_funcs.xsl"/>
+  <xsl:import href="/org/eolang/funcs/lineno.xsl"/>
+  <xsl:import href="/org/eolang/funcs/defect-context.xsl"/>
+  <xsl:output encoding="UTF-8" method="xml"/>
+  <xsl:template match="/">
+    <defects>
+      <xsl:for-each select="//o[not(eo:abstract(.)) and parent::o[starts-with(@base, '.')] and not(starts-with(@base, '.')) and not(text())]">
+        <xsl:message select="."/>
+        <defect>
+          <xsl:variable name="line" select="eo:lineno(@line)"/>
+          <xsl:attribute name="line">
+            <xsl:value-of select="$line"/>
+          </xsl:attribute>
+          <xsl:if test="$line = '0'">
+            <xsl:attribute name="context">
+              <xsl:value-of select="eo:defect-context(.)"/>
+            </xsl:attribute>
+          </xsl:if>
+          <xsl:attribute name="severity">
+            <xsl:text>warning</xsl:text>
+          </xsl:attribute>
+          <xsl:text>Object </xsl:text>
+          <xsl:if test="@name">
+            <xsl:value-of select="@name"/>
+            <xsl:text> </xsl:text>
+          </xsl:if>
+          <xsl:text>can be merged with its parent</xsl:text>
+        </defect>
+      </xsl:for-each>
+    </defects>
+  </xsl:template>
+</xsl:stylesheet>
diff --git a/src/main/resources/org/eolang/motives/refs/base-must-be-merged.md b/src/main/resources/org/eolang/motives/refs/base-must-be-merged.md
new file mode 100644
index 000000000..c5868aeeb
--- /dev/null
+++ b/src/main/resources/org/eolang/motives/refs/base-must-be-merged.md
@@ -0,0 +1,64 @@
+# '@base' attributes of objects must be merged if possible
+
+In [XMIR], the object must be merged with parent if the following
+conditions are met:
+
+1. Object is not abstract
+2. Attribute `@base` of parent object should start with dot
+3. Attribute `@base` object should not start with dot
+4. Object should not have data
+5. Object should not have inner objects
+
+Incorrect:
+
+```xml
+<o base=".foo">
+  <o base=".bar">
+    <o base="x"/>
+  </o>
+</o>
+```
+
+Correct:
+
+```xml
+<o base="x.bar.foo"/>
+```
+
+Correct:
+
+```xml
+<o base=".foo">
+  <o base=".bar"/>
+</o>
+```
+
+Correct:
+
+```xml
+<o base=".foo">
+  <o/>
+</o>
+```
+
+Correct:
+
+```xml
+<o base=".foo">
+  <o base="bar">
+    A1-B2-C3-D4-E5
+  </o>
+</o>
+```
+
+Correct:
+
+```xml
+<o base=".foo">
+  <o base="bar">
+    <o base="baz"/>
+  </o>
+</o>
+```
+
+[XMIR]: https://news.eolang.org/2022-11-25-xmir-guide.html
diff --git a/src/test/resources/org/eolang/lints/packs/single/base-must-be-merged/catches-not-merged-objects.yaml b/src/test/resources/org/eolang/lints/packs/single/base-must-be-merged/catches-not-merged-objects.yaml
new file mode 100644
index 000000000..d39df581a
--- /dev/null
+++ b/src/test/resources/org/eolang/lints/packs/single/base-must-be-merged/catches-not-merged-objects.yaml
@@ -0,0 +1,16 @@
+# SPDX-FileCopyrightText: Copyright (c) 2016-2025 Objectionary.com
+# SPDX-License-Identifier: MIT
+---
+sheets:
+  - /org/eolang/lints/refs/base-must-be-merged.xsl
+asserts:
+  - /defects[count(defect[@severity='warning'])=1]
+  - /defects/defect[@line='2']
+document: |
+  <object>
+    <o base=".foo">
+      <o base=".bar">
+        <o base="x" line="2"/>
+      </o>
+    </o>
+  </object>
diff --git a/src/test/resources/org/eolang/lints/packs/single/base-must-be-merged/no-merge-if-base-starts-with-dot.yaml b/src/test/resources/org/eolang/lints/packs/single/base-must-be-merged/no-merge-if-base-starts-with-dot.yaml
new file mode 100644
index 000000000..870658d9a
--- /dev/null
+++ b/src/test/resources/org/eolang/lints/packs/single/base-must-be-merged/no-merge-if-base-starts-with-dot.yaml
@@ -0,0 +1,13 @@
+# SPDX-FileCopyrightText: Copyright (c) 2016-2025 Objectionary.com
+# SPDX-License-Identifier: MIT
+---
+sheets:
+  - /org/eolang/lints/refs/base-must-be-merged.xsl
+asserts:
+  - /defects[count(defect[@severity='warning'])=0]
+document: |
+  <object>
+    <o base=".foo">
+      <o base=".bar"/>
+    </o>
+  </object>
diff --git a/src/test/resources/org/eolang/lints/packs/single/base-must-be-merged/no-merge-if-object-has-data.yaml b/src/test/resources/org/eolang/lints/packs/single/base-must-be-merged/no-merge-if-object-has-data.yaml
new file mode 100644
index 000000000..9de923dc3
--- /dev/null
+++ b/src/test/resources/org/eolang/lints/packs/single/base-must-be-merged/no-merge-if-object-has-data.yaml
@@ -0,0 +1,15 @@
+# SPDX-FileCopyrightText: Copyright (c) 2016-2025 Objectionary.com
+# SPDX-License-Identifier: MIT
+---
+sheets:
+  - /org/eolang/lints/refs/base-must-be-merged.xsl
+asserts:
+  - /defects[count(defect[@severity='warning'])=0]
+document: |
+  <object>
+    <o base=".foo">
+      <o base="bar">
+        A1-B2-C3-D4-E5
+      </o>
+    </o>
+  </object>
diff --git a/src/test/resources/org/eolang/lints/packs/single/base-must-be-merged/no-merge-if-object-has-inner-object.yaml b/src/test/resources/org/eolang/lints/packs/single/base-must-be-merged/no-merge-if-object-has-inner-object.yaml
new file mode 100644
index 000000000..81abae977
--- /dev/null
+++ b/src/test/resources/org/eolang/lints/packs/single/base-must-be-merged/no-merge-if-object-has-inner-object.yaml
@@ -0,0 +1,15 @@
+# SPDX-FileCopyrightText: Copyright (c) 2016-2025 Objectionary.com
+# SPDX-License-Identifier: MIT
+---
+sheets:
+  - /org/eolang/lints/refs/base-must-be-merged.xsl
+asserts:
+  - /defects[count(defect[@severity='warning'])=0]
+document: |
+  <object>
+    <o base=".foo">
+      <o base="bar">
+        <o base="baz"/>
+      </o>
+    </o>
+  </object>
diff --git a/src/test/resources/org/eolang/lints/packs/single/base-must-be-merged/no-merge-if-object-is-abstract.yaml b/src/test/resources/org/eolang/lints/packs/single/base-must-be-merged/no-merge-if-object-is-abstract.yaml
new file mode 100644
index 000000000..fe8433d23
--- /dev/null
+++ b/src/test/resources/org/eolang/lints/packs/single/base-must-be-merged/no-merge-if-object-is-abstract.yaml
@@ -0,0 +1,13 @@
+# SPDX-FileCopyrightText: Copyright (c) 2016-2025 Objectionary.com
+# SPDX-License-Identifier: MIT
+---
+sheets:
+  - /org/eolang/lints/refs/base-must-be-merged.xsl
+asserts:
+  - /defects[count(defect[@severity='warning'])=0]
+document: |
+  <object>
+    <o base=".foo">
+      <o/>
+    </o>
+  </object>
diff --git a/src/test/resources/org/eolang/lints/packs/single/base-must-be-merged/prints-name-of-not-merged-object.yaml b/src/test/resources/org/eolang/lints/packs/single/base-must-be-merged/prints-name-of-not-merged-object.yaml
new file mode 100644
index 000000000..b4f54d1f4
--- /dev/null
+++ b/src/test/resources/org/eolang/lints/packs/single/base-must-be-merged/prints-name-of-not-merged-object.yaml
@@ -0,0 +1,15 @@
+# SPDX-FileCopyrightText: Copyright (c) 2016-2025 Objectionary.com
+# SPDX-License-Identifier: MIT
+---
+sheets:
+  - /org/eolang/lints/refs/base-must-be-merged.xsl
+asserts:
+  - /defects/defect[contains(text(), 'abracadabra')]
+document: |
+  <object>
+    <o base=".foo">
+      <o base=".bar">
+        <o base="x" name="abracadabra"/>
+      </o>
+    </o>
+  </object>