@vv Thanks much for your suggestion.
Let me give a little more detail: My problem arises from expression involving constructs like this:
(and the real ones are a lot longer that this snippet). The difficulties for taylor are then obvious: id d1kQ1 is negative (in this case) the sqrt can get imaginary. This should be easily solved by assuming dkQ1 to be within (-1..+1), say (which would be totally acceptable for my case). Except that I find mtaylor to barf at the assumptions, or ignore them, or just return unevaluated (I found the behaviour to be not reproducible). Sometimes regular taylor works better.
I am enclosing a worksheet that demonstrates some of the issues. It also shows my attempt to use vv's mseries, which was not successfull. I spare MaplePrimes listing it here as it involves too many endless numbers (all of course generated expressions).
I cooked up a quick & dirty one:
for i from 1 to numelems(vars) do
but it has some issues. First and forward, it does not control the order the way mtaylor does in that it will keep bilinear and higher-order products as it only expands by one variable at any given time. I can fix that with a final mtaylor (which will work on the result) but certaily have not proven yet that the end result is correct. I also don't like the for...next loop.