What does stata's laglimit mean? I just saw an explanation to xtabond2 here
xtabond2 depvar varlist [if exp] [in range] [weight] [, level(#)
                svmat twostep robust cluster(varname) noconstant small
                noleveleq orthogonal gmmopt [gmmopt ...] ivopt [ivopt ...]
                pca components(#) artests(#) arlevels h(#) nodiffsargan
                nomata]

with the explanation in gmmstyle():
The optional laglimits(a b) suboption can override these defaults: for the transformed equation, lagged levels dated t-a to t-b are used as instruments, while for the levels equation, the first-difference dated t-a+1 is normally used.
I am quite confused about this. Can anyone explain that with a concrete example?
 A: A useful heuristic is that complicated (long helpfile) AND popular community-contributed/user-written Stata commands usually have a Stata Journal article that explains things in more detail. Sometimes there are also website or more informal documents instead that you can find using Google.
From the SJ paper on xtabond2 contains some good examples:

The laglimits() suboption overrides the defaults on lag range. For
example, gmmstyle(w, laglimits(2 .)) specifies lags 2 and longer for
the transformed equation and lag 1 for the levels equation, which is
the standard treatment for endogenous variables. In general,
laglimits(a b) requests lags a through b of the levels as
instruments for the transformed data and lag a−1 of the differences
for the levels data. a and b can each be missing (“.”). a defaults to
1 and b to infinity, so that laglimits(. .) is equivalent to leaving
the suboption out altogether. a and b can even be negative, implying
forward “lags”. If a>b, xtabond2 swaps their values. Because the
gmmstyle() varlist allows time-series operators, there are many
routes to the same specification. For example, if w1 is predetermined
and w2 endogenous, then instead of gmmstyle(w1) gmmstyle(w2, laglimits(2 .)), one could simply type gmmstyle(w1 L.w2).

The Stata manual covers time-series operators (like lags and lag differences) in great detail here.
