[...] the 'laterals', are semi-stopped. There is a true stoppage at the central point of articulation, but the breath is allowed to escape through the two side passages or through one of them [...] - Sapir (1921), a pag.51
Laterals are possible in many distinct positions. They may be unvoiced (the Welsh 'll' is an example ) as well as voiced. - Sapir (1921), a pag.51