@Override
    public CharSequence getText(CharSequence text) {
        if (children().isEmpty()) {
            return "";
        }
        StringBuilder str = new StringBuilder();
        for (SpanNode node : children()) {
            CharSequence childText = node.getText(text);
            if (childText != null) {
                str.append(node.getText(text));
            }
        }
        return str;
    }
Returns the text that is covered by this SpanNode.

@param text the input text
@return the text that is covered by this SpanNode.
document/src/main/java/com/yahoo/document/annotation/SpanList.java