Don't use 'current' if 'from' is not relative.

lib/src/context.dart

Index: lib/src/context.dart
diff --git a/lib/src/context.dart b/lib/src/context.dart
index a3efd95a9cbd4c4b5829df32149857911d4f1028..7a210c60d92769acc5bd242cbeceb653b07d5794 100644
--- a/lib/src/context.dart
+++ b/lib/src/context.dart
@@ -324,7 +324,11 @@ class Context {
   /// "/", no path can be determined. In this case, a [PathException] will be
   /// thrown.
   String relative(String path, {String from}) {
-    from = from == null ? current : this.join(current, from);
+    if (from == null) {
+      from = current;
+    } else if (this.isRelative(from) || this.isRootRelative(from)) {

[Bob Nystrom, 2015/02/18 17:09:08]

Document this:

// Avoid calling [current] since it is slow and calling join() when [from] is
absolute does nothing.

+      from = this.join(current, from);
+    }
 
     // We can't determine the path from a relative path to an absolute path.
     if (this.isRelative(from) && this.isAbsolute(path)) {