diff --git a/includes/Cite.php b/includes/Cite.php
index d8af7d34d..b12545203 100644
--- a/includes/Cite.php
+++ b/includes/Cite.php
@@ -61,6 +61,12 @@ class Cite {
 	 */
 	private const CACHE_DURATION_ONFETCH = 18000;
 
+	/**
+	 * Wikitext attribute name for Book Referencing.
+	 * TODO: Still under discussion.
+	 */
+	public const REFINES_ATTRIBUTE = 'refines';
+
 	/**
 	 * Datastructure representing <ref> input, in the format of:
 	 * <code>
@@ -391,6 +397,7 @@ class Cite {
 	 *  "group" : Group to which it belongs. Needs to be passed to <references /> too.
 	 *  "follow" : If the current reference is the continuation of another, key of that reference.
 	 *  "dir" : set direction of text (ltr/rtl)
+	 *  "refines": Points to a named reference which serves as the context for this reference.
 	 *
 	 * @param string[] $argv The argument vector
 	 * @return (string|false|null)[] An array with exactly four elements, where each is a string on
@@ -398,6 +405,8 @@ class Cite {
 	 * @return-taint tainted
 	 */
 	private function refArg( array $argv ) {
+		global $wgCiteBookReferencing;
+
 		$group = null;
 		$key = null;
 		$follow = null;
@@ -438,6 +447,11 @@ class Cite {
 			$group = $argv['group'];
 			unset( $argv['group'] );
 		}
+		if ( $wgCiteBookReferencing && isset( $argv[self::REFINES_ATTRIBUTE] ) ) {
+			// TODO: Extract the name and return it.
+			// $refines = trim( $argv[self::REFINES_ATTRIBUTE] );
+			unset( $argv[self::REFINES_ATTRIBUTE] );
+		}
 
 		if ( $argv !== [] ) {
 			// Invalid key
diff --git a/tests/parser/citeParserTests.txt b/tests/parser/citeParserTests.txt
index db689c4fb..d5dd509f9 100644
--- a/tests/parser/citeParserTests.txt
+++ b/tests/parser/citeParserTests.txt
@@ -1709,3 +1709,38 @@ wgFragmentMode=['legacy']
 <p><sup about="#mwt2" class="mw-ref" id="cite_ref-füllen_1-0" rel="dc:references" typeof="mw:Extension/ref" data-mw='{"name":"ref","attrs":{"name":"füllen"},"body":{"id":"mw-reference-text-cite_note-füllen-1"}}'><a href="./Parser_test#cite_note-füllen_1-1" style="counter-reset: mw-Ref 1;"><span class="mw-reflink-text">[1]</span></a></sup></p>
 <ol class="mw-references references" typeof="mw:Extension/references" about="#mwt3" data-mw='{"name":"references","attrs":{}}'><li about="#cite_note-füllen-1" id="cite_note-füllen-1"><a href="./Parser_test#cite_ref-füllen-0" rel="mw:referencedBy"><span class="mw-linkback-text">↑ </span></a> <span id="mw-reference-text-cite_note-füllen-1" class="mw-reference-text" data-parsoid="{}">[bar]</span></li></ol>
 !! end
+
+!! test
+Refines tag rejected by default
+!! config
+wgCiteBookReferencing=false
+!! wikitext
+<ref name="parent">[foo]</ref>
+<ref refines="parent">[bar]</ref>
+!! html/php
+<p><sup id="cite_ref-parent_1-0" class="reference"><a href="#cite_note-parent-1">&#91;1&#93;</a></sup>
+<span class="error mw-ext-cite-error" lang="en" dir="ltr">Cite error: Invalid <code>&lt;ref&gt;</code> tag;
+</p>
+invalid names, e.g. too many</span><div class="mw-references-wrap"><ol class="references">
+<li id="cite_note-parent-1"><span class="mw-cite-backlink"><a href="#cite_ref-parent_1-0">↑</a></span> <span class="reference-text">[foo]</span>
+</li>
+</ol></div>
+!! end
+
+!! test
+Refines tag allowed with feature flag set
+!! config
+wgCiteBookReferencing=true
+!! wikitext
+<ref name="parent">[foo]</ref>
+<ref refines="parent">[bar]</ref>
+!! html/php
+<p><sup id="cite_ref-parent_1-0" class="reference"><a href="#cite_note-parent-1">&#91;1&#93;</a></sup>
+</p>
+<sup id="cite_ref-2" class="reference"><a href="#cite_note-2">&#91;2&#93;</a></sup><div class="mw-references-wrap"><ol class="references">
+<li id="cite_note-parent-1"><span class="mw-cite-backlink"><a href="#cite_ref-parent_1-0">↑</a></span> <span class="reference-text">[foo]</span>
+</li>
+<li id="cite_note-2"><span class="mw-cite-backlink"><a href="#cite_ref-2">↑</a></span> <span class="reference-text">[bar]</span>
+</li>
+</ol></div>
+!! end