However, when Gestuno was first used, at the WFD congress in Bulgaria in 1976, it was incomprehensible to deaf participants.[10] Subsequently, it was developed informally by deaf and hearing interpreters, and came to include more grammar — especially linguistic features that are thought to be universal among sign languages, such as role shifting and the use of classifiers. Additionally, the vocabulary was gradually replaced by more iconic signs and loan signs from different sign languages.[citation needed]