Select an option from a drop-down using an option locator.

Option locators provide different ways of specifying options of an HTML Select element (e.g. for selecting a specific option, or for asserting that the selected option satisfies a specification). There are several forms of Select Option Locator.

   * label=labelPattern: matches options based on their labels, i.e. the visible text. (This is the default.)
   * label=regexp:^[Oo]ther
    value=valuePattern: matches options based on their values.
        value=other
   * id=id: matches options based on their ids.
        id=option1
   * index=index: matches an option based on its index (offset from zero).
        index=2

If no option locator prefix is provided, the default behaviour is to match on label.