Create jspsych-html-button-response.md

docs/markdown_docs/plugins/jspsych-html-button-response.md

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+# jspsych-html-button-response
+
+This plugin displays HTML content and records responses generated with a button click.The stimulus can be displayed until a response is given, or for a pre-determined amount of time. The trial can be ended 
+automatically if the subject has failed to respond within a fixed length of time. The button itself can be customized using 
+HTML formatting.
+
+## Parameters
+
+This table lists the parameters associated with this plugin. Parameters with a default value of *undefined* must be specified. 
+Other parameters can be left unspecified if the default value is acceptable.
+
+Parameter | Type | Default Value | Description
+----------|------|---------------|------------
+stimulus | HTML string | undefined | The string to be displayed.
+choices | Array of strings | [] | The button labels.
+button_html | HTML string | `'<button class="jspsych-btn">%choice%</button>'` | A template of HTML for generating the button elements. You can override this to create customized buttons of various kinds. The string `%choice%` will be changed to the corresponding element of the `choices` array. You may also specify an array of strings, if you need different HTML to render for each button. If you do specify an array, the `choices` array and this array must have the same length. The HTML from position 0 in the `button_html` array will be used to create the button for element 0 in the `choices` array, and so on.
+prompt | string | "" | This string can contain HTML markup. Any content here will be displayed below the stimulus. The intention is that it can be used to provide a reminder about the action the subject is supposed to take (e.g. which key to press).
+trial_duration | numeric | -1 | How long to wait for the subject to make a response before ending the trial in milliseconds. If the subject fails to make a response before this timer is reached, the subject's response will be recorded as -1 for the trial and the trial will end. If the value of this parameter is -1, the trial will wait for a response indefinitely.
+margin_vertical | String | '0px' | Vertical margin of the button.
+margin_horizontal | String | '8px' | Horizontal margin of button.
+response_ends_trial | boolean | true | If true, then the trial will end whenever the subject makes a response (assuming they make their response before the cutoff specified by the `trial_duration` parameter). If false, then the trial will continue until the value for `timing_response` is reached. You can use this parameter to force the subject to view a stimulus for a fixed amount of time, even if they respond before the time is complete.
+trial_ends_after_audio | Boolean | false | If true, then the trial will end as soon as the audio file finishes playing.
+
+## Data Generated
+
+In addition to the [default data collected by all plugins](overview#datacollectedbyplugins), this plugin collects the following data for each trial.
+
+Name | Type | Value
+-----|------|------
+rt | numeric | The response time in milliseconds for the subject to make a response. The time is measured from when the stimulus first appears on the screen until the subject's response.
+button_pressed | numeric | Indicates which button the subject pressed. The first button in the `choices` array is 0, the second is 1, and so on.
+
+## Examples
+
+#### Displaying question until subject gives a response
+
+```javascript
+var trial = {
+	type: 'html-button-response',
+	stimulus: '<p>Running</p>',
+	choices: ['Healthy', 'Unhealthy'],
+	prompt: "<p>Is this activity healthy or unhealthy?</p>"
+};
+```