                         self._view.value(forSymbol: symbol) {
                         return value
                     }
-                    throw SymbolError("\(symbol) not found", for: symbol)
+                    throw SymbolError("Undefined symbol `\(symbol)`", for: symbol)
                 }
             }
         }

        var size = CGSize.zero
        for child in children where !child.isHidden {
            if !child.widthDependsOnParent {
                size.width = max(
                    size.width,
                    try child.cgFloatValue(forSymbol: "left") + child.cgFloatValue(forSymbol: "width")
                )
            }
            if !child.heightDependsOnParent {
                size.height = max(
                    size.height,
                    try child.cgFloatValue(forSymbol: "top") + child.cgFloatValue(forSymbol: "height")
                )
            }
        }
        // If zero, fill superview

        if let result = _heightDependsOnParent {
            return result
        }
        if value(forSymbol: "height", dependsOn: "parent.height") {
            _heightDependsOnParent = true
            return true
        }
