function arabicWordStartCheck(contextParams) {
    var char = contextParams.current;
    var prevChar = contextParams.get(-1);
    return (
        // ? arabic first char
        (prevChar === null && isArabicChar(char)) ||
        // ? arabic char preceded with a non arabic char
        (!isArabicChar(prevChar) && isArabicChar(char))
    );
}
Apply single substitution format 1
@param {Array} substitutions substitutions
@param {any} tokens a list of tokens
@param {number} index token index