Minor review of redirect-related code

Notably, I finally settled for implicit priority of
0, but now negative priority values are allowed.

src/js/codemirror/ubo-static-filtering.js

@@ -187,7 +187,7 @@ CodeMirror.defineMode('ubo-static-filtering', function() {
             /[$,]redirect(-rule)?=$/.test(string.slice(0, pos))
         ) {
             style = 'value';
-            let end = parser.skipUntil(
+            const end = parser.skipUntil(
                 parserSlot,
                 parser.commentSpan.i,
                 parser.BITComma

src/js/redirect-engine.js

@@ -291,11 +291,11 @@ RedirectEngine.prototype.freeze = function() {
 
 /******************************************************************************/
 
-RedirectEngine.prototype.tokenToURL = function(fctxt, token) {
-    const asDataURI = token.charCodeAt(0) === 0x25 /* '%' */;
-    if ( asDataURI ) {
-        token = token.slice(1);
-    }
+RedirectEngine.prototype.tokenToURL = function(
+    fctxt,
+    token,
+    asDataURI = false
+) {
     const entry = this.resources.get(this.aliases.get(token) || token);
     if ( entry === undefined ) { return; }
     this.resourceNameRegister = token;

src/js/static-filtering-parser.js

@@ -1164,13 +1164,15 @@ const Parser = class {
 
     static parseRedirectValue(arg) {
         let token = arg.trim();
-        let priority = 10;
-        const match = /:\d+$/.exec(token);
+        let priority = 0;
+        const asDataURI = token.charCodeAt(0) === 0x25 /* '%' */;
+        if ( asDataURI ) { token = token.slice(1); }
+        const match = /:-?\d+$/.exec(token);
         if ( match !== null ) {
             token = token.slice(0, match.index);
             priority = parseInt(token.slice(match.index + 1), 10);
         }
-        return { token, priority };
+        return { token, priority, asDataURI };
     }
 
     static parseQueryPruneValue(arg) {

src/js/static-net-filtering.js

@@ -4236,12 +4236,13 @@ FilterContainer.prototype.redirectRequest = function(fctxt) {
     const directives = this.matchAndFetchModifiers(fctxt, 'redirect-rule');
     // No directive is the most common occurrence.
     if ( directives === undefined ) { return; }
+    const highest = directives.length - 1;
     // More than a single directive means more work.
-    if ( directives.length !== 1 ) {
+    if ( highest !== 0 ) {
         directives.sort(FilterContainer.compareRedirectRequests);
     }
     // Redirect to highest-ranked directive
-    const directive = directives[directives.length - 1];
+    const directive = directives[highest];
     if ( (directive.bits & AllowAction) === 0 ) {
         const { token } =
             FilterContainer.parseRedirectRequestValue(directive.modifier);