add description of web app loading feature

README.md

@@ -46,3 +46,34 @@ above. That framework will immediately reveal many crashers and discrepancies
 in output of the "dsp" methods of external classes. Developers can then use
 the output of those tests to get a better sense of the scope of the work and
 prioritize which libraries to refactor first.
+
+API for HTML5 Web Apps
+----------------------
+
+Goal: create an API and simple user interface for loading a web app
+that is linked to a Pd patch.
+
+Details: Currently Pd patches are essentially just an HTML page with
+an inline SVG which displays an editable diagram. It should be possible
+for the user to instead open an arbitrary HTML document that contains
+a web app which communicates using a javascript API with a Pd patch.
+
+Implementation suggestion: since the current pdgui.js module already has
+an interface for sending messages to the Pd backend, we should probably
+leverage that to communicate from the web app to Pd. Then it's only
+necessary to add a feature that allows a Pd Patch to send messages back
+to the web app.
+
+The user should then be able to load an HTML file using the existing
+File->Open dialog. Then the web app will need something like the following
+interface:
+
+* ability to send messages to Pd (already exists)
+* ability to tell Pd to load a particular patch in the same directory as
+the web app (or perhaps using Pd's search path).
+* ability to close a Pd patch
+* ability to specify whether the patch we're loading should default to
+  being visible or hidden
+* ability to set callbacks for the web app to receive the following events:
+  * the Pd patch we wanted to open has loaded
+  * the Pd patch we loaded has closed