Added cell unfocus event canceller API

IPython/html/static/notebook/js/cell.js

@@ -48,7 +48,7 @@ var IPython = (function (IPython) {
         this.cell_id = utils.uuid();
         this._options = options;
 
-        // For JS VM engines optimisation, attributes should be all set (even
+        // For JS VM engines optimization, attributes should be all set (even
         // to null) in the constructor, and if possible, if different subclass
         // have new attributes with same name, they should be created in the
         // same order. Easiest is to create and set to null in parent class.
@@ -57,6 +57,10 @@ var IPython = (function (IPython) {
         this.cell_type = this.cell_type || null;
         this.code_mirror = null;
 
+        // This is a list of callbacks that are called when a cell's textual 
+        // region is unfocused.  If one of the callbacks returns True, the cell 
+        // unfocus event will be ignored.  Callbacks will be passed no arguments.
+        this.cancel_unfocus_callbacks = [];
 
         this.create_element();
         if (this.element !== null) {
@@ -264,6 +268,17 @@ var IPython = (function (IPython) {
         }
     };
 
+    /**
+     * Check if this cell's unfocus event was legit.
+     */
+    Cell.prototype.should_cancel_unfocus = function () {
+        // Try user registered callbacks.
+        for (var i=0; i<this.cancel_unfocus_callbacks.length; i++) {
+            if (this.cancel_unfocus_callbacks[i]()) { return true; }
+        }
+        return false;
+    };
+
     /**
      * Focus the cell in the DOM sense
      * @method focus_cell

IPython/html/static/notebook/js/codecell.js

@@ -418,6 +418,17 @@ var IPython = (function (IPython) {
         return cont;
     };
 
+    /**
+     * Check if this cell's unfocus event was legit.
+     */
+    CodeCell.prototype.should_cancel_unfocus = function () {
+        // Call base
+        if (IPython.Cell.prototype.should_cancel_unfocus.apply(this)) { return true; }
+
+        // Cancel this unfocus event if the cell completer is open.
+        return (this.completer && this.completer.is_visible());
+    };
+
     /**
      * Focus the editor area so a user can type
      * @method focus_editor

IPython/html/static/notebook/js/notebook.js

@@ -55,6 +55,12 @@ var IPython = (function (IPython) {
         this.notebook_name_blacklist_re = /[\/\\:]/;
         this.nbformat = 3; // Increment this when changing the nbformat
         this.nbformat_minor = 0; // Increment this when changing the nbformat
+
+        // This is a list of callbacks that are called when a cell's textual 
+        // region is unfocused.  If one of the callbacks returns True, the cell 
+        // unfocus event will be ignored.  Callbacks will be passed one argument,
+        // the cell instance.
+        this.cancel_unfocus_callbacks = [];
         this.style();
         this.create_elements();
         this.bind_events();
@@ -581,11 +587,8 @@ var IPython = (function (IPython) {
         var cell = this.get_cell(index);
         if (!cell) {return;}
 
-        // Only respect the blur event if the tooltip and autocompleter are
-        // not visible.
-        var tooltip_visible = IPython.tooltip && IPython.tooltip.is_visible();
-        var completer_visible = cell.completer && cell.completer.is_visible();
-        if (!tooltip_visible && !completer_visible) {
+        // Check if this unfocus event is legit.
+        if (!this.should_cancel_unfocus(cell)) {
             // In Firefox the focus event is called before the blur event.  In 
             // other words, two cells elements may be focused at any given time.
             // This has been witnessed on Win7 x64 w/ FF 25.  Here we only put the
@@ -603,6 +606,26 @@ var IPython = (function (IPython) {
         }
     };
 
+    Notebook.prototype.should_cancel_unfocus = function (cell) {
+        // Determine whether or not the unfocus event should be aknowledged.
+
+        // If the tooltip is visible, ignore the unfocus.
+        var tooltip_visible = IPython.tooltip && IPython.tooltip.is_visible();
+        if (tooltip_visible) { return true; }
+        
+        // Try user registered callbacks.
+        for (var i=0; i<this.cancel_unfocus_callbacks.length; i++) {
+            if (this.cancel_unfocus_callbacks[i](cell)) { return true; }
+        }
+
+        // Check the cell's should_cancel_unfocus method.
+        if (cell.should_cancel_unfocus !== undefined && cell.should_cancel_unfocus()) {
+            return true;
+        } else {
+            return false;
+        }
+    };
+
     // Cell movement
 
     /**