Quick question on trgLang

Hi all,

 

As we’ve started implementing the standard, there are, of course, differing interpretations of some of the wording in the spec. Can the TC as a group please help me understand
 the following:

 

4.2.2.1 xliff

…

Constraints

·        
The

trgLang attribute is REQUIRED if and only if the
XLIFF Document contains

<target> elements that are children of

<segment> or

<ignorable>.

Does this constraint mean:

·        
The

trgLang attribute is REQUIRED
if the XLIFF Document contains

<target> elements that are children of

<segment> or

<ignorable>,
otherwise it is optional. 

Or does it mean:

·        
The

trgLang attribute is REQUIRED
only if the XLIFF Document contains

<target> elements that are children of

<segment> or

<ignorable>,
otherwise it MUST not be present. 

For example, is this legal?

<xliff version=”2.0” srcLang=”en-us” trgLang=”de-de”>

…

   <unit id=”1”>

      <segment id=”1”>Hello World</segment>

   </unit>

I think it is, but want to be sure I am reading this correctly. In a more general question, is there a reason why the verbiage “if and only if” is used throughout
 the spec and not just “if”?

Thanks,

Ryan