[lmi] Style question: when should "a_" prefix be used?

[Vadim Zeitlin]

 Hello,

 I'm looking at the sources trying to formulate the various style rules,
but I just can't understand what is the rule for using "a_" prefix for the
function arguments. Initially I thought that it was limited only to the
ctor arguments, but this isn't really the case, and luckily so, because if
it were, I'd have trouble finding a rationale for it, considering that I've
just formulated a rule saying that all class members (and they only) should
have a trailing underscore in their names, ensuring that they can't clash
with the function arguments.

 But now I just can't formulate any rule at all. E.g. why does the recently
added SequenceParser class ctor use "a_" for all of its arguments except
the first one?

 Thanks in advance for any help,
VZ