Implement Multi-value aka Picklist (Multi-Select)

Tested this and it works a treat. Thankyou.

Key-value pairs MUST be specified as "safe_key|Some readable option". Use of only alphanumeric characters and underscores is recommended in keys. One option per line. Option groups may be specified with . <> can be used to insert items at the root of the menu after specifying a group.

0|All
1|Asia
2|North America
3|Europe
4|Latin America
5|Rest of world

Regions of Interest:<select  id="00N20000002M5fo" multiple="multiple" name="00N20000002M5fo" title="Regions of Interest"><option value="All">All</option>
<option value="Asia">Asia</option>
<option value="North America">North America</option>
<option value="Europe">Europe</option>
<option value="Latin America">Latin America</option>
<option value="Rest of world">Rest of world</option>
</select><br>

I've tried, but not work.

works， safe_key|Some readable option must be the same for my case.
need to specific salesforce id as the salesforce key.

Thanks.

I'll lay it out very plainly with an example just because it took me some time to figure this out:

My Drupal form with a checklist named I am interested in generated html similar to the following:
----------------------

<div class="form-item webform-component webform-component-checkboxes" id="webform-component-i-am-interested-in">
  <label for="edit-submitted-i-am-interested-in">I am interested in </label>
 <div id="edit-submitted-i-am-interested-in" class="form-checkboxes"><div class="form-item form-type-checkbox form-item-submitted-i-am-interested-in-Scheduling-a-demo">
 <input type="checkbox" id="edit-submitted-i-am-interested-in-1" name="submitted[i_am_interested_in][Scheduling a demo]" value="Scheduling a demo" class="form-checkbox">  <label class="option" for="edit-submitted-i-am-interested-in-1">Scheduling a demo </label>
</div>
<div class="form-item form-type-checkbox form-item-submitted-i-am-interested-in-2">
 <input type="checkbox" id="edit-submitted-i-am-interested-in-2" name="submitted[i_am_interested_in][2]" value="2" class="form-checkbox">  <label class="option" for="edit-submitted-i-am-interested-in-2">Joining the community </label>
........

From one of the checkbox items, you take 'i_am_interested_in' as the key: ( submitted[this_part] )
----------------------
In salesforce, when you generate the web-to-lead form with the picklist, you'll get something like:
Label:<select id="00N400000002SLqJ"......
That 'id' is what you use for the 'value'.
----------------------
So, in this example, configuration of a multi-select list / picklist / checklist on the Drupal Salesforce Webform config page uses:
key: i_am_interested_in (retrieved as above)
value: 00N400000002SLqJ

The form will then send the 'key' to your form's submitted items to salesforce