Marking Operations as Safe
  - Operation can be marked as safe:
    <operation
. . . safe='true' . . . > 
  - "Safe": Requester agent incurs no new obligation by invoking the
operation
 
  
    - Analogous to HTTP GET
 
    - Can be implemented by HTTP GET
     
  
  - Permits:
 
  
    - Pre-fetch
 
    - Re-fetch
 
    - Safe exploration