Contract
Parameter key	Default value	Type
on	req with ekind of expression	string
new_path	opt with ekind of expression	string
message	""	string
title	opt
significance	0	type.<range_of min=0.0 max=10.0 include_max=true number_type=number/>
old_still_works	false	boolean
changed_on	opt	datetime
why	opt	string
developer	opt	string
internal_note	opt	string
error_prefix	' Change req '	string
id	opt
backward_compatibility_code	opt
Parameter kind	Default value	Type
Other unkeyed arguments	opt with ekind of mixed	wob

Water Contract

<class change
  on            =req=string=ekind.expression
  new_path      =opt=string=ekind.expression
  message       =""=string
  title         =opt
  significance  =0=<type.range_of min=0.0 max=10.0 include_max=true number_type=number/>
  old_still_works=false=boolean
  changed_on    =opt=datetime
  why           =opt=string
  developer     =opt=string
  internal_note =opt=string
  error_prefix  ='<DIV><BIG><FONT&amp;#32;color="green">Change&amp;#32;req</FONT></BIG></DIV>'
  id            =opt
  backward_compatibility_code=opt
  _other_unkeyed=opt=wob=ekind.mixed="_other_unkeyed"
  _other_unkeyed=opt=wob=ekind.mixed="_other_unkeyed"
/>

Change indicates to Water that a method or class has been changed from its previous implementation in such a way that its 'contract' is different such that existing calls to that method or class may no longer work or behave as expected. During most development it is not worth the overhead to use change . However, after software has been finalized and released to users, change can help inform the users of method changes. Two cases: 1. Deprecate a parameter of a method or class. A type that returns an error when an argument is passed in. An optional string arg is the error message to display. 2. Deprecate an entire method or class Put as a default value. A path or symbol to deprecate plus an optional string to display when the field is accessed. You may create a stub that returns an error as a placeholder for a function not yet implemented.