Support math rendering on MFM (#3260)

src/mfm/parse/elements/math.ts

@@ -0,0 +1,20 @@
+/**
+ * Math
+ */
+
+export type TextElementMath = {
+	type: 'math';
+	content: string;
+	formula: string;
+};
+
+export default function(text: string) {
+	const match = text.match(/^\$(.+?)\$/);
+	if (!match) return null;
+	const math = match[0];
+	return {
+		type: 'math',
+		content: math,
+		formula: match[1]
+	} as TextElementMath;
+}