code: private int findStartOfWord(@NonNull CharSequence text, int index) {
          int wordStart = index;
          while (wordStart > 0 && mTokenizer != null && !mTokenizer.isWordBreakingChar(text.charAt(wordStart - 1))) {
              wordStart--;
          }
          return wordStart;
      }
docs: Helper utility to determine the beginning of a word using the current tokenizer.
  
  @param text  the text to examine
  @param index index of the cursor in the text
  @return  index of the beginning of the word in text (will be less than or equal to index)