docs: better document the expression operator regexp

Author: DylanPiercey

src/states/EXPRESSION.ts

@@ -223,11 +223,29 @@ export const EXPRESSION: StateDefinition<ExpressionMeta> = {
 };
 
 function buildOperatorPattern(isConcise: boolean) {
-  const binary = `[*%<&^|?:]|=[=<>]|/[^*/>]|\\.(?=\\s)|\\bin(?:stanceof)(?=\\s+[^=/,;:>])`;
-  const unary = `!|a(?:sync|wait)|class|function|new|typeof|void`;
-  const lookAheadPattern = `\\s*(?:${binary}|\\+|${
-    isConcise ? "-[^-]" : "-"
-  }${`|>${isConcise ? "" : "[>=]"}`})\\s*|\\s+(?=[${isConcise ? "" : "["}{(])`;
+  const binary =
+    "[*%<&^|?:]" + // Any of these characters can always continue an expression
+    "|=[=>]" + // We only continue after an equals if it is => or ==
+    "|/[^*/>]" + // We only continue after a forward slash if it isn't //, /* or />
+    "|\\.(?=\\s)" + // We only continue after a period if it's followed by a space
+    "|\\bin(?:stanceof)(?=\\s+[^=/,;:>])"; // We only continue after word operators (instanceof/in) when they are not followed by a terminator
+  const unary =
+    "!" +
+    "|a(?:sync|wait)" +
+    "|class" +
+    "|function" +
+    "|new" +
+    "|typeof" +
+    "|void";
+  const lookAheadPattern =
+    "\\s*(?:" +
+    binary +
+    "|\\+" + // any number of plus signs are ok.
+    `|-${isConcise ? "[^-]" : ""}` + // in concise mode only consume minus signs if not --
+    `|>${isConcise ? "" : "[>=]"}` + // in html mode only consume closing angle brackets if it is >= or >>
+    ")\\s*" +
+    `|\\s+(?=[${isConcise ? "" : "["}{(])`; // if we have spaces followed by an opening bracket, we'll consume the spaces and let the expression state handle the brackets
+
   const lookBehindPattern = `(?<=${unary}|${binary}|[^-]-|[^+]\\+)`;
   return new RegExp(`${lookAheadPattern}|${lookBehindPattern}`, "y");
 }