2.3.1 [W3C-HTML51] Section 5.6.2 Making entire documents editable: The designMode IDL attribute

E0001: If the designMode IDL attribute matches the value “inherit” then designMode is enabled if the parent designMode is enabled, and disabled if the parent designMode is disabled

The specification states:

 7.6.2 Making entire documents editable: The designMode IDL attribute
     ...
     The designMode IDL attribute on the Document object takes two values, "on" and "off". 
     On setting, the new value must be compared in an ASCII case-insensitive manner to 
     these two values; if it matches the "on" value, then designMode must be enabled, and 
     if it matches the "off" value, then designMode must be disabled. Other values must be 
     ignored.

EdgeHTML Mode

If the designMode IDL attribute matches the value “inherit” then designMode is enabled if the parent designMode is enabled, and disabled if the parent designMode is disabled.