Initial docs about validation

source/developers/development_validation.markdown

@@ -0,0 +1,67 @@
+---
+layout: page
+title: "Validate the input"
+description: "Validation of entries in configuration.yaml"
+date: 2016-08-11 20:00
+sidebar: true
+comments: false
+sharing: true
+footer: true
+---
+
+The `configuration.yaml` file contains the configuration options for components and platforms. To ensure that the given configuration provided by the user is valid we use [voluptuous](https://pypi.python.org/pypi/voluptuous) to check it. Certain entries are optional or could be required for the setup of a platform or a component. Others must be of a certain type or out of an already defined list. This will ensure that the users are notified if something is wrong with a platform or component setup before Home Assistant is running.
+
+Beside the [voluptuous](https://pypi.python.org/pypi/voluptuous) default types are a bunch of custom types available. To get a full overview take a look at the [config_validation.py](https://github.com/home-assistant/home-assistant/blob/master/homeassistant/helpers/config_validation.py) helper.
+
+- Types: `string`, `byte`, and `boolean`
+- Entity ID: `entity_id` and `entity_ids`
+- Numbers: `small_float` and `positive_int`
+- Time: `time`, `time_zone`
+- Misc: `template`, `slug`, `temperature_unit`, `latitude`, `longitude`, `isfile`, `sun_event`, `ensure_list`, and `icon`
+ 
+To validate plaforms using [MQTT](/components/mqtt/) there are `valid_subscribe_topic` and `valid_publish_topic` present.
+
+### {% linkable_title Snippets %} 
+
+This section contains a couple of snippets for the validation we use.
+
+### {% linkable_title Default name %} 
+
+```python
+DEFAULT_NAME = 'Sensor name'
+
+PLATFORM_SCHEMA = vol.Schema({
+    ...
+    vol.Optional(CONF_NAME, default=DEFAULT_NAME): cv.string,
+```
+
+### {% linkable_title Port %} 
+
+As all port numbers are coming out of the range 1 till 65535 a range check should be performed. 
+
+```python
+DEFAULT_PORT = 993
+
+PLATFORM_SCHEMA = vol.Schema({
+    [...]
+    vol.Optional(CONF_PORT, default=DEFAULT_PORT):
+        vol.All(vol.Coerce(int), vol.Range(min=1, max=65535)),
+```
+
+### {% linkable_title Sensor types %} 
+
+If a sensor has a pre-defined list of available options it should be tested if the configuration entry matches it.
+
+```python
+SENSOR_TYPES = {
+    'article_cache': ('Article Cache', 'MB'),
+    'average_download_rate': ('Average Speed', 'MB/s'),
+}
+
+PLATFORM_SCHEMA = vol.Schema({
+    ....
+    vol.Optional(CONF_MONITORED_VARIABLES, default=[]):
+        [vol.In(SENSOR_TYPES)],
+```
+
+