code: private void updateSelectionIfRequired(final int selStart, final int selEnd) {
          MentionsEditable text = getMentionsText();
          MentionSpan startMentionSpan = text.getMentionSpanAtOffset(selStart);
          MentionSpan endMentionSpan = text.getMentionSpanAtOffset(selEnd);
          boolean selChanged = false;
          int start = selStart;
          int end = selEnd;
          if (text.getSpanStart(startMentionSpan) < selStart && selStart < text.getSpanEnd(startMentionSpan)) {
              start = text.getSpanStart(startMentionSpan);
              selChanged = true;
          }
          if (text.getSpanStart(endMentionSpan) < selEnd && selEnd < text.getSpanEnd(endMentionSpan)) {
              end = text.getSpanEnd(endMentionSpan);
              selChanged = true;
          }
          if (selChanged) {
              setSelection(start, end);
          }
      }
docs: Don't allow user to set starting position or ending position of selection within the mention.