Fields such as the user selection list (oppo_assigneduserid) are examples of a type of field known as an Intelligent Select
The intelligent select in edit mode displays additional structures, a search box and a magnifying glass image.
The search box associated with the intelligent select or user select or team select is named in this way fieldname
so the field for the assigned user id field in Opportunities would be:
The HTML structures that create the magnifying glass button and the search box are both contained within the HTML span tags that mark the data content of the field. In the example of the Opportunity Assigned Userid this would be:
This means that in clientside code it is very easy to turn on and off the whole display of the field structure addressing the properties of the span and the _Dataoppo_assigneduserid
See the article "Identification (ID) of Checkbox Fields in Clientside Code
". Another discussion of Intelligent Selects can be found here "Using SearchSQL to limit data returned by selection lists