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

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

    }

    private func computeExplicitWidth() throws -> CGFloat? {
        if !_evaluating.contains("width"),
            !_evaluating.contains("height") || !value(forSymbol: "width", dependsOn: "height") {
            return try cgFloatValue(forSymbol: "width")
        }
        if expressions["contentSize.width"] != nil, !_evaluating.contains("contentSize.width") {
