The zero-based index into the input sources list specifying the current one in effect. The value is automatically capped to remain in the range [0, sources_length) as long as the sources list isn't empty.
Sarrerako iturburuen zerrendan dagoen zero balioan oinarritutako indizea unekoa zehaztuz. Balioa automatikoki mugatzen da barrutian [0, sources_length) mantentzeko iturburuen zerrenda hutsik ez dagoen heinean.