Fixes #25

core/shared/src/main/scala/reftree/dot/DotEncoding.scala

@@ -30,8 +30,10 @@ private[dot] sealed trait DotAttrEncoding extends LabelledProductTypeClassCompan
         if (headEnc.encoded.isEmpty) {
           ct.encoding(tail)
         } else {
+          // The 'URL' attribute must remain in uppercase otherwise it will be ignored.
+          val encodedName = if (name == "URL") name else name.toLowerCase
           Chunk.join(" ")(
-            Chunk.join("=")(Chunk(name.toLowerCase), headEnc),
+            Chunk.join("=")(Chunk(encodedName), headEnc),
             ct.encoding(tail)
           )
         }

core/shared/src/main/scala/reftree/dot/Graph.scala

@@ -38,6 +38,7 @@ object Node {
   case class Attrs(
     shape: Option[String] = None,
     tooltip: Option[String] = None,
+    URL: Option[String] = None,
     color: Option[Color] = None,
     fontName: Option[String] = None,
     fontColor: Option[Color] = None

core/shared/src/main/scala/reftree/graph/Graphs.scala

@@ -32,11 +32,11 @@ object Graphs {
       depth: Int
     ): Seq[GraphStatement] = tree match {
       case r @ RefTree.Ref(_, id, children, _) ⇒
-        Seq(Primitives.node(r, color, anchorId, namespace)) ++
+        Seq(Primitives.node(r, color, anchorId, namespace, options.nodeURLs.get(id), options.nodeTips.get(id))) ++
           children.filterNot(_.elideRefs).flatMap(c ⇒ inner(c.value, color, None, namespace, depth + 1)) ++
           children.zipWithIndex.flatMap { case (c, i) ⇒ Primitives.edge(id, c.value, i, color, namespace) }
       case _ if depth == 0 ⇒
-        Seq(Primitives.node(tree, color, anchorId, namespace))
+        Seq(Primitives.node(tree, color, anchorId, namespace, None, None))
       case _ ⇒
         Seq.empty
     }

core/shared/src/main/scala/reftree/graph/Primitives.scala

@@ -29,7 +29,7 @@ object Primitives {
     Seq(captionNode, captionEdge)
   }
 
-  def node(tree: RefTree, color: Color, anchorId: Option[String], namespace: Seq[String]): Node = {
+  def node(tree: RefTree, color: Color, anchorId: Option[String], namespace: Seq[String], url: Option[String], tip: Option[String]): Node = {
     val background = if (tree.highlight) color.opacify(0.2) else defaultBackground
     val labelContent: Seq[Row] = tree match {
       case ref: RefTree.Ref ⇒
@@ -51,9 +51,9 @@ object Primitives {
       cellSpacing = Some(0), cellPadding = Some(6), cellBorder = Some(0), columns = Some("*"),
       bgColor = Some(background), style = Some("rounded")
     ))
-    val tooltip = anchorId.map(a ⇒ s"anchor-$a")
+    val tooltip = tip.orElse(anchorId.map(a ⇒ s"anchor-$a"))
     val id = namespaced(tree.id, namespace)
-    Node(id, label, Node.Attrs(fontColor = Some(color), color = Some(color), tooltip = tooltip))
+    Node(id, label, Node.Attrs(fontColor = Some(color), color = Some(color), tooltip = tooltip, URL = url))
   }
 
   private def cellLabel(tree: RefTree, elideRefs: Boolean = false): Html = tree match {

core/shared/src/main/scala/reftree/render/Options.scala

@@ -7,12 +7,16 @@ import java.time.Duration
  * Options for rendering static diagrams
  *
  * @param verticalSpacing vertical spacing to set for Graphviz
+ * @param nodeURLs map of node ID to a URL
+ * @param nodeTips map of node ID to a node tooltip overriding the anchor tooltip, if defined
  * @param palette a sequence of colors to be used
  * @param font the font for text rendering
  * @param density the desired image density, in pixels per inch
  */
 case class RenderingOptions(
   verticalSpacing: Double = 0.8,
+  nodeURLs: Map[String, String] = Map.empty,
+  nodeTips: Map[String, String] = Map.empty,
   palette: IndexedSeq[Color] = Array(
     Color.fromRgbaString("#104e8b"),
     Color.fromRgbaString("#228b22"),

site/src/main/tut/Guide.md

@@ -80,6 +80,26 @@ val renderer = Renderer(
 )
 ```
 
+**For SVG rendering (JVM, Scala.js):**
+
+It is possible to specify for each `RefTree.Ref`
+a hyperlink URL and a tooltip text
+by providing associating to the `RefTree.Ref.id` a URL string
+or a tooltip string respectively.
+
+```scala
+import reftree.render._
+import reftree.diagram._
+
+val renderer = Renderer(
+  renderingOptions = RenderingOptions(
+    density = 75,
+    nodeURLs = Map("1" -> "http://www.example.org", "2" -> "http://www.foobar.org"),
+    nodeTips = Map("1" -> "example", "2" -> "foobar")),
+  format = "svg"
+)
+```
+
 There are two ways to use renderers:
 
 **JVM**