input. More calculations became available and partial analyses were performed but a new complete analysis was done in [@Bijnens:2011tb]. The main improvement of the refitting done in this review over [@Bijnens:2011tb] is a more extensive use of knowledge of the NNLO LECs as discussed in Sec. \[sec:nf3fits\]. A minor improvement is the inclusion of some newer $K_{l4}$ data. The data and theoretical input used in the [$n_f=3$]{} fits beyond that already used for the [$n_f=2$]{}results are described in Sec. \[sec:input3\]. Our fitting and the new central values for the LECs are given in Sec. \[sec:nf3fits\]. The evidence for resonance saturation of both NLO and NNLO LECs is discussed in Sec. \[sec:resonance\]. The quality of the fits and the convergence of the chiral expansion are discussed in Sec. \[sec:convergence\].

The LECs that show up in extensions with dynamical photons and leptons cannot be determined from phenomenology directly but need further treatment. We collect the known results in Sec. \[sec:photons\] where we pay close attention to the correct inclusion of short-distance contributions. For those involving the weak nonleptonic interaction we only give a short list of the main references in Sec. \[sec:other\] and refer to the recent review [@Cirigliano:2011ny] for more references 