MDL-56809 boost: Add template context info

theme/boost/templates/core_form/element-select.mustache

+{{!
+    This file is part of Moodle - http://moodle.org/
+
+    Moodle 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.
+
+    Moodle 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 Moodle.  If not, see <http://www.gnu.org/licenses/>.
+}}
+{{!
+    @template core_form/element-select
+
+    Simple select form element template.
+
+    Context variables required for this template:
+    * id - Element id,
+    * name - Element name,
+    * label -  Element label,
+    * multiple - multi select?,
+    * checked - checked?,
+    * error - Is there an error associated with this element?,
+    * size - Element size,
+    * value - Element value,
+    * helpbutton - Helpbutton,
+    * hiddenlabel - Element hidden flag,
+    * frozen - Element frozen flag,
+    * hardfrozen - Element hard fronzen flag,
+    * extraclasses - Extra classes assocaited,
+    * type - Element type,
+    * attributes - Element attributes,
+    * options - [
+        {
+            text - Option text,
+            value - Option value,
+            selected - Selected?,
+            disabled - Disabled?,
+            optionattributes - Option attributes
+        }
+    ]
+
+    Example context (json):
+    {
+        "element": {
+            "id": "id_maildisplay",
+            "name": "maildisplay",
+            "label": null,
+            "multiple": null,
+            "checked": null,
+            "error": null,
+            "size": null,
+            "value": null,
+            "helpbutton": "",
+            "hiddenlabel": false,
+            "frozen": false,
+            "hardfrozen": false,
+            "extraclasses": null,
+            "type": "select",
+            "attributes": "",
+            "options": [
+                {
+                    "text": "Hide my email address from everyone",
+                    "value": 0,
+                    "selected": false,
+                    "disabled": false,
+                    "optionattributes": ""
+                },
+                {
+                    "text": "Allow everyone to see my email address",
+                    "value": 1,
+                    "selected": true,
+                    "disabled": false,
+                    "optionattributes": ""
+                },
+                {
+                    "text": "Allow only other course members to see my email address",
+                    "value": 2,
+                    "selected": false,
+                    "disabled": false,
+                    "optionattributes": ""
+                }
+            ]
+        }
+    }
+}}
 {{< core_form/element-template }}
     {{$element}}
         {{^element.frozen}}