RE: [xliff-comment] placeholder id should not be required

I don't recall a discussion around making the id of inline codes
optional, although it seems like a very reasonable request. 

I do remember a discussion around removing the <x/>, <bx/>, and <ex/>
tags since <ph/>, <bpt/>, and <ept/>, respectively, can replace those.
However, the reverse is not true (<x/> cannot replace all uses of <ph>).
For that reason, it is preferrable to use <ph/> over <x/>. 

As an explanation: The <ph> tag and <x/> tags mark unpaired codes. The
<ph> tag can have as content the marked up code while the <x/> actually
replaces the code. For example, the following 'foo' formatted text
contains a bookmark code preceding the word 'bookmark'.

    This text contains a %%bm;1%%bookmark.

If <x/> is used, the <x/> replaces the bookmark code, '%%bm;1%%', which
would be stored in a skeleton file. The resultant xliff would be as
follows.

    <source>This text contains a <x id="1" ctype="bookmark"
clone="no"/>bookmark.</source>

If <ph> is used, the <ph> marks up the bookmark code, which would
remain as content of the <ph> tag. The resultant xliff would be as
follows.

    <source>This text contains a <ph id="1" ctype="bookmark"
clone="no"/>%%bm;1%%</ph>bookmark.</source>

cheers,
john