Thank you all for your contribution! 
Yes indeed, the (a) was just to mark a footnote, sorry it was confusing. 

@Hugh, the solution you offer lets us print or display "conieci", but not represent the fact that there is a conjecture here, and also the factual link between the reading in the Vulgate and the editor's hypothesis is less evident. 
What about using the certainty element? Something like: 

        <lem>meo<certainty cert="high" locus="value"><desc>uestro <title>Vulg.</title></desc></certainty></lem>
        <rdg wit="#P #V #H #E"><abbr>m</abbr></rdg>

What I like about the above is also that it would let us print or display the apparatus according to the age-old conventions of critical editions - something I am very attentive to maintain, even in born-digital editions. 

Any thoughts? It would be good to reach a community's agreement on the way to encode such very frequent phenomena in critical editions.

Best wishes, 

----- Mail original -----
De: "Hugh Cayless" <[log in to unmask]>
À: [log in to unmask]
Envoyé: Dimanche 3 Mai 2015 20:07:25
Objet: Re: Encoding conjecture in critical apparatus

Ah, that worries me much less then :-). Sorry for the confusion.

Nolite timere, pusillus grex, complacuit patri <app><lem source="#ed">meo</lem><note>conieci</note><rdg wit="#codd"><abbr>m<am>.</am></abbr></rdg><rdg wit="#Vulg">vestro</rdg></app> dare uobis regnum.

@source="#ed" indicates that the lemma is the editor’s own conjecture, #ed being a pointer to a bibl in sourceDesc, probably, since you’re encoding the edition. 

I’ll add that if you’re wanting to encode the form of the apparatus as printed in the text, then you probably want to do the apparatus as <notes> rather than (or in addition to) using <app>.

> On May 3, 2015, at 13:48 , Lou Burnard <[log in to unmask]> wrote:
> I think the (a) is a footnote indicator and nothing to do with the text.
> Sent from my Samsung Galaxy Tab®|PRO
> -------- Original message --------
> From: Hugh Cayless 
> Date:05/03/2015 16:48 (GMT+00:00) 
> To: [log in to unmask] 
> Subject: Re: Encoding conjecture in critical apparatus 
> I’m rather puzzled by this. Is meo(a) meant to convey that "mea" is a possible expansion of "m."? I don’t think that works at all in Latin, since "patri" is masculine, but I don’t see (without more context) how else to read it.
> I’d probably do something like:
> Nolite timere, pusillus grex, complacuit patri <app><lem source="#ed"><choice><seg cert="high">meo</seg><seg cert="low">mea</seg></choice></lem><rdg wit="#codd"><abbr>m<am>.</am></abbr></rdg><rdg wit="#Vulg">vestro</rdg></app> dare uobis regnum.
> Perhaps "meo(a)" means something like "The only possible expansions of "m." are "meo" and "mea". I give the latter for completeness’ sake, but parenthesize it because it is impossible." In which case, I might do it differently. I might also restrict the <choice> only to o(a), depending on my encoding policy, so <lem>me<choice><seg cert="high>o</seg><seg cert="low">a</seg></choice></lem> or something like that.
> Hope this helps…
> Hugh
> > On May 2, 2015, at 18:17 , Burghart Marjorie <[log in to unmask]> wrote:
> > 
> > Dear all, 
> > I would like to encode an existing critical edition, where this is found: 
> > 
> > 
> > Text: 
> > Nolite timere, pusillus grex, complacuit patri meo(a) dare uobis regnum. 
> > 
> > Apparatus: 
> > (a) meo] conieci, m. codd., uestro Vulg.
> > 
> > Some explanations: this means that the wor "meo" in the sentence is a conjecture of the editor ("conieci"). 
> > All the manuscripts bear the same abbreviated reading, "m." ("m. codd."). 
> > But this sentence is actually a biblical quotation, and in the Latun Bible, the Vulgate, the reading here is "uestro" ("uestro Vulg."). This is why the editor thinks "m."stands for "meo", i.e. also a pronoum but for a different person, which makes perfect sense. 
> > 
> > How would you guys encode this? 
> > 
> > Cheers, 
> > Marjorie