diff --git a/emcc.c b/emcc.c
index 3cb92f0..7c436c1 100644
--- a/emcc.c
+++ b/emcc.c
@@ -3,7 +3,10 @@
  * end for Puzzles.
  *
  * The Javascript parts of this system live in emcclib.js and
- * emccpre.js.
+ * emccpre.js. It also depends on being run in the context of a web
+ * page containing an appropriate collection of bits and pieces (a
+ * canvas, some buttons and links etc), which is generated for each
+ * puzzle by the script html/jspage.pl.
  */
 
 /*
diff --git a/emcclib.js b/emcclib.js
index 6c37c9b..cbdd668 100644
--- a/emcclib.js
+++ b/emcclib.js
@@ -2,7 +2,11 @@
  * emcclib.js: one of the Javascript components of an Emscripten-based
  * web/Javascript front end for Puzzles.
  *
- * The other parts of this system live in emcc.c and emccpre.js.
+ * The other parts of this system live in emcc.c and emccpre.js. It
+ * also depends on being run in the context of a web page containing
+ * an appropriate collection of bits and pieces (a canvas, some
+ * buttons and links etc), which is generated for each puzzle by the
+ * script html/jspage.pl.
  *
  * This file contains a set of Javascript functions which we insert
  * into Emscripten's library object via the --js-library option; this
diff --git a/emccpre.js b/emccpre.js
index e2986da..fb58a6a 100644
--- a/emccpre.js
+++ b/emccpre.js
@@ -2,7 +2,11 @@
  * emccpre.js: one of the Javascript components of an Emscripten-based
  * web/Javascript front end for Puzzles.
  *
- * The other parts of this system live in emcc.c and emcclib.js.
+ * The other parts of this system live in emcc.c and emcclib.js. It
+ * also depends on being run in the context of a web page containing
+ * an appropriate collection of bits and pieces (a canvas, some
+ * buttons and links etc), which is generated for each puzzle by the
+ * script html/jspage.pl.
  *
  * This file contains the Javascript code which is prefixed unmodified
  * to Emscripten's output via the --pre-js option. It declares all our