diff --git a/src/dyna-rules.html b/src/dyna-rules.html
index 87bc10a0c..12353f354 100644
--- a/src/dyna-rules.html
+++ b/src/dyna-rules.html
@@ -48,6 +48,8 @@
 <script src="lib/codemirror/addon/merge/merge.js"></script>
 <script src="lib/codemirror/addon/selection/active-line.js"></script>
 
+<script src="js/codemirror/ubo-dynamic-filtering.js"></script>
+
 <script src="js/vapi.js"></script>
 <script src="js/vapi-common.js"></script>
 <script src="js/vapi-client.js"></script>
diff --git a/src/js/codemirror/ubo-dynamic-filtering.js b/src/js/codemirror/ubo-dynamic-filtering.js
new file mode 100644
index 000000000..cc493e484
--- /dev/null
+++ b/src/js/codemirror/ubo-dynamic-filtering.js
@@ -0,0 +1,187 @@
+/*******************************************************************************
+
+    uBlock Origin - a browser extension to block requests.
+    Copyright (C) 2019-present Raymond Hill
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see {http://www.gnu.org/licenses/}.
+
+    Home: https://github.com/gorhill/uBlock
+*/
+
+/* global CodeMirror */
+
+'use strict';
+
+CodeMirror.defineMode('ubo-dynamic-filtering', ( ) => {
+
+    const validSwitches = new Set([
+        'no-strict-blocking:',
+        'no-popups:',
+        'no-cosmetic-filtering:',
+        'no-remote-fonts:',
+        'no-large-media:',
+        'no-csp-reports:',
+        'no-scripting:',
+    ]);
+    const validSwitcheStates = new Set([
+        'true',
+        'false',
+    ]);
+    const validTypes = new Set([
+        '*',
+        '3p',
+        'image',
+        'inline-script',
+        '1p-script',
+        '3p-script',
+        '3p-frame',
+    ]);
+    const validActions = new Set([
+        'block',
+        'allow',
+        'noop',
+    ]);
+    const reIsNotHostname = /[:/#?*]/;
+    const tokens = [];
+
+    const isSwitchRule = ( ) => {
+        const token = tokens[0];
+        return token.charCodeAt(token.length-1) === 0x3A /* ':' */;
+    };
+
+    const isURLRule = ( ) => {
+        return /^[\w-_]+:\/\/[^/]+\//.test(tokens[1]);
+    };
+
+    const skipToEnd = (stream, style = null) => {
+        stream.skipToEnd();
+        return style;
+    };
+
+    const token = stream => {
+        if ( stream.sol() ) { tokens.length = 0; }
+        stream.eatSpace();
+        const match = stream.match(/\S+/);
+        if ( Array.isArray(match) === false ) {
+            return skipToEnd(stream);
+        }
+        if ( tokens.length === 4 ) {
+            return skipToEnd(stream, 'error');
+        }
+        const token = match[0];
+        tokens.push(token);
+        // Field 1: per-site switch or hostname
+        if ( tokens.length === 1 ) {
+            if ( isSwitchRule(token) ) {
+                if ( validSwitches.has(token) === false ) {
+                    return skipToEnd(stream, 'error');
+                }
+            } else if ( reIsNotHostname.test(token) && token !== '*' ) {
+                return skipToEnd(stream, 'error');
+            }
+            return null;
+        }
+        // Field 2: hostname or url
+        if ( tokens.length === 2 ) {
+            if ( isSwitchRule(tokens[0]) ) {
+                if ( reIsNotHostname.test(token) && token !== '*' ) {
+                    return skipToEnd(stream, 'error');
+                }
+            }
+            if (
+                reIsNotHostname.test(token) &&
+                token !== '*' &&
+                isURLRule(token) === false
+            ) {
+                return skipToEnd(stream, 'error');
+            }
+            return null;
+        }
+        // Field 3
+        if ( tokens.length === 3 ) {
+            if ( isSwitchRule(tokens[0]) ) {
+                if ( validSwitcheStates.has(token) === false ) {
+                    return skipToEnd(stream, 'error');
+                }
+                return null;
+            }
+            if ( isURLRule(tokens[1]) === false ) {
+                if (
+                    tokens[1] !== '*' && token !== '*' ||
+                    tokens[1] === '*' && validTypes.has(token) === false
+                ) {
+                    return skipToEnd(stream, 'error');
+                }
+            }
+            return null;
+        }
+        // Field 4
+        if ( tokens.length === 4 ) {
+            if (
+                isSwitchRule(tokens[0]) ||
+                validActions.has(token) === false
+            ) {
+                return skipToEnd(stream, 'error');
+            }
+            return null;
+        }
+        return skipToEnd(stream);
+    };
+
+    return { token };
+});
+
+/*
+Code below is to address
+https://github.com/uBlockOrigin/uMatrix-issues/issues/128
+
+But this needs fixing because glitchiness in some cases.
+I may end up having to create a custom merge view rather
+than using the existing CodeMirror one.
+
+CodeMirror.registerHelper('fold', 'ubo-dynamic-filtering', (cm, start) => {
+    function isHeader(lineNo) {
+        const tokentype = cm.getTokenTypeAt(CodeMirror.Pos(lineNo, 0));
+        return tokentype && /\bheader\b/.test(tokentype);
+    }
+
+    function headerLevel(lineNo, line, nextLine) {
+        let match = line && line.match(/^#+/);
+        if (match && isHeader(lineNo)) return match[0].length;
+        match = nextLine && nextLine.match(/^[=\-]+\s*$/);
+        if (match && isHeader(lineNo + 1)) return nextLine[0] === '=' ? 1 : 2;
+        return 100;
+    }
+
+    const firstLine = cm.getLine(start.line);
+    let nextLine = cm.getLine(start.line + 1);
+    const level = headerLevel(start.line, firstLine, nextLine);
+    if ( level === 100 ) { return; }
+
+    const lastLineNo = cm.lastLine();
+    let end = start.line,
+        nextNextLine = cm.getLine(end + 2);
+    while ( end < lastLineNo ) {
+        if ( headerLevel(end + 1, nextLine, nextNextLine) <= level ) { break; }
+        ++end;
+        nextLine = nextNextLine;
+        nextNextLine = cm.getLine(end + 2);
+    }
+
+    return {
+        from: CodeMirror.Pos(start.line, firstLine.length),
+        to: CodeMirror.Pos(end, cm.getLine(end).length),
+    };
+});
+*/