For discussion, see note on ${{\mathit K}}_{{{\mathit \ell}}3}$ form factors in the ${{\mathit K}^{\pm}}$ section of the Particle Listings above. Because the semileptonic branching fraction is smaller in ${{\mathit K}_S^0}$ than ${{\mathit K}_L^0}$ by the ratio of the mean lives, the ${{\mathit K}_S^0}$ semileptonic form factor has so far been measured only in the ${{\mathit K}_{{{e3}}}}$ mode using the linear expansion $\mathit f_{+}(\mathit t$) = $\mathit f_{+}$(0) (1 + $\lambda _{+}\mathit t$ $/{{\mathit m}^{2}}_{{{\mathit \pi}^{+}}}$), which gives the vector form factor ${{\mathit f}_{{+}}}({{\mathit t}}$) relative to its value at ${{\mathit t}}$ = 0.