Add clickable anchors to HTML docs

Fixes spring-projectsgh-525

Author: Phillip Webb

spring-boot-docs/src/main/docbook/css/manual.css

@@ -311,3 +311,31 @@ div.navheader {
 div.navfooter {
 	border-top: 1px solid #CCCCCC;
 }
+
+.title {
+	margin-left: -1em;
+	padding-left: 1em;
+}
+
+.title>a {
+	position: absolute;
+	visibility: hidden;
+	display: block;
+	font-size: 0.85em;
+	margin-top: 0.05em;
+	margin-left: -1em;
+	vertical-align: text-top;
+	color: black;
+}
+
+.title>a:before {
+	content: "\00A7";
+}
+
+.title:hover>a,.title>a:hover,.title:hover>a:hover {
+	visibility: visible;
+}
+
+.title:focus>a,.title>a:focus,.title:focus>a:focus {
+	outline: 0;
+}

spring-boot-docs/src/main/docbook/xsl/html.xsl

@@ -114,4 +114,27 @@ under the License.
 			<xsl:apply-templates mode="titlepage.mode"/>
 		</div>
 	</xsl:template>
+
+	<!-- Title Links -->
+	<xsl:template name="anchor">
+		<xsl:param name="node" select="."/>
+		<xsl:param name="conditional" select="1"/>
+		<xsl:variable name="id">
+			<xsl:call-template name="object.id">
+				<xsl:with-param name="object" select="$node"/>
+			</xsl:call-template>
+		</xsl:variable>
+		<xsl:if test="$conditional = 0 or $node/@id or $node/@xml:id">
+			<xsl:element name="a">
+				<xsl:attribute name="name">
+					<xsl:value-of select="$id"/>
+				</xsl:attribute>
+				<xsl:attribute name="href">
+					<xsl:text>#</xsl:text>
+					<xsl:value-of select="$id"/>
+				</xsl:attribute>
+			</xsl:element>
+		</xsl:if>
+	</xsl:template>
+
 </xsl:stylesheet>