Defines supported values used for controlling which elements within a page will be used as sources when harvesting links.
        
        
- Source:
Members
A :number
    Harvest links from the href attribute of  elements.
    Type:
- number
- Source:
FRAME :number
    Harvest links from the src attribute of  elements. 
Frames with an aria-hidden value equal to 'true' or a computed style containing a display value equal to 'none' or a visibility not equal to 'visible' will be ignored.
    Type:
- number
- Source:
IFRAME :number
    Harvest links from the src attribute of 
    Type:
- number
- Source:
META :number
    Harvest links from the content attribute of  elements that have an http-equiv attribute value of 'refresh'.
    Type:
- number
- Source: