diff --git a/index.html b/index.html
index 913aa769..5fab7653 100644
--- a/index.html
+++ b/index.html
@@ -7,8 +7,8 @@
   <link rel=stylesheet href='style/jstree/style.css'>
   <link rel=stylesheet href='node_modules/golden-layout/src/css/goldenlayout-base.css'>
   <link rel=stylesheet href='node_modules/golden-layout/src/css/goldenlayout-light-theme.css'>
-  <style id=col_stl></style>
-  <style id=col_sample_stl></style>
+  <style id=col_stl></style><!--src/prf_col.js injects css here-->
+  <style id=col_sample_stl></style><!--and here-->
 </head>
 <body>
 <noscript>JavaScript is not enabled.</noscript>
diff --git a/sample-extensions/syntax-in-comments.js b/sample-extensions/syntax-in-comments.js
index c57053f1..267b10ac 100644
--- a/sample-extensions/syntax-in-comments.js
+++ b/sample-extensions/syntax-in-comments.js
@@ -1,6 +1,10 @@
-// To use this extension:
-//   export RIDE_JS=/path/to/file.js
-// before running RIDE.
+//To use this extension:
+//  export RIDE_JS=/path/to/file.js
+//before starting RIDE.
+//Go to Preferences>Colours, select Token Type: ACME Number and style it.
+//Open an editor and type
+//  ⍝1: abc 123
+//"123" should appear different.
 CodeMirror.defineMIME('text/apl-comments','acme')
 CodeMirror.defineMode('acme',function(){ // https://codemirror.net/doc/manual.html#modeapi
   return{
diff --git a/src/prf_col.js b/src/prf_col.js
index 68a40d3c..68e2184a 100644
--- a/src/prf_col.js
+++ b/src/prf_col.js
@@ -1,8 +1,10 @@
 //Preferences > Colours
+//Here we generate CSS based on the user's preferences and put it in <style id=col_stl> (see ../index.html)
+//Same for <style id=col_sample_stl> - this one controls the display of the sample text, before pressing Apply or OK.
 ;(function(){'use strict'
-
 var G=[],H={} //G:syntax highlighting groups; H:reverse lookup dict for G
 var q //dict of DOM elements whose ids start with "col_", keyed by the rest of the id
+//D.addSynGrps(...) is the API for extensions, see ../sample-extensions/syntax-in-comments.js
 D.addSynGrps=function(x){G=G.concat(x);H={};for(var i=0;i<G.length;i++)H[G[i].t]=i;SCMS&&updStl()}
 D.addSynGrps([
   //t: token type, a short key for storing customisations
