In chevron samples of ferroelectric liquid crystals (FLC) the twisted molecular organization is confined either to the upper part of chevron with lower part untwisted orvice versa. Therefore two different director configurations with respect to the chevron interface can coexist and they can be mediated by so called inversion line. The structure of the inversion line is proposed using the simpliest approximation of FLC elasticity and its basic properties like their creation and ineraction with unwinding lines is discussed.