private String appendFirstColumn(String expression, StringBuilder b) {
        if (firstColumnLength == 0) return expression;

        while (expression.charAt(0) == ' ')
            expression = expression.substring(1);

        if (expression.charAt(0) == '\t') {
            int tab2 = expression.indexOf('\t', 1);
            if (tab2 >= 0) {
                String firstColumn = expression.substring(1, tab2);
                b.append(asSize(firstColumnLength, firstColumn)).append(" ");
                return expression.substring(tab2 + 1);
            }
        }
        appendIndent(firstColumnLength + 1, b);
        return expression;
    }
Returns the position of the end of a balanced chunk of at most the given size, or 0 if there is no such chunk
vespajlib/src/main/java/com/yahoo/text/ExpressionFormatter.java