raise on non-symbolic and non-lowercase :id (#740)

resolves #695

lib/phlex/sgml.rb

@@ -396,6 +396,10 @@ def __attributes__(attributes, buffer = +"")
 					raise ArgumentError.new("Unsafe attribute name detected: #{k}.")
 				end
 
+				if lower_name.to_sym == :id && k != :id
+					raise ArgumentError.new(":id attribute should only be passed as a lowercase symbol.")
+				end
+
 				case v
 				when true
 					buffer << " " << name

test/phlex/view/lowercase_symbolic_id_guard.test.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+describe Phlex::SGML do
+	extend ViewHelper
+
+	with "non lowercase id" do
+		view do
+			def view_template
+				div(iD: "a")
+			end
+		end
+
+		it "raises" do
+			expect { output }.to raise_exception(Phlex::ArgumentError)
+		end
+	end
+
+	with "non symbolic id" do
+		view do
+			def view_template
+				div("id" => "a")
+			end
+		end
+
+		it "raises" do
+			expect { output }.to raise_exception(Phlex::ArgumentError)
+		end
+	end
+end