def create_table_start_l(data: GTData, use_longtable: bool) -> str:
    """
    Create the table start component for LaTeX output.

    This function generates the LaTeX code that signifies the start of the table. The output is
    different depending on whether the table uses the `longtable` environment or not.

    Parameters
    ----------
    data : GTData
        The GTData object that contains all the information about the table.

    Returns
    -------
    str
        The LaTeX code that signifies the start of the table.
    """

    # Determine if there are any source notes; if any, add a `\setlength` command that will pull up
    # the minipage environment for the footer block

    # Get all source notes as a list
    source_notes = data._source_notes

    if len(source_notes) > 0:
        longtable_post_length = "\\setlength{\\LTpost}{0mm}\n"

    else:
        longtable_post_length = ""

    # Get the column alignments for the visible columns as a list of `col_defs`
    col_defs = [align[0] for align in data._boxhead._get_default_alignments()]

    # If a table width is specified, add an extra column
    # space to fill in enough space to match the width
    extra_sep = ""

    # Obtain the table width value from the `table_width` options value
    table_width = data._options.table_width.value

    if table_width != "auto":
        extra_sep = "@{\\extracolsep{\\fill}}"

    # determine string for table width if using tabular* environment
    hdr_tabular = ""

    if not use_longtable:
        # we need to use the extracolsep here for tabular* regardless of width
        extra_sep = "@{\\extracolsep{\\fill}}"

        if table_width.endswith("%"):
            tw = float(table_width.replace("%", ""))

            tw_frac = tw / 100

            hdr_tabular = f"\\begin{{tabular*}}{{{tw_frac}\\linewidth}}{{"

        elif table_width.endswith("px"):
            width_in_pt = convert_to_pt(table_width)
            hdr_tabular = f"\\begin{{tabular*}}{{{width_in_pt}pt}}{{"

        else:
            hdr_tabular = "\\begin{tabular*}{\\linewidth}{"

    # Generate setup statements for table including default left
    # alignments and vertical lines for any stub columns
    table_start = "".join(
        [
            longtable_post_length if use_longtable else "",
            "\\begin{longtable}{" if use_longtable else hdr_tabular,
            extra_sep,
            "".join(col_defs),
            "}",
        ]
    )

    return table_start

    Create the table start component for LaTeX output.

    This function generates the LaTeX code that signifies the start of the table. The output is
    different depending on whether the table uses the `longtable` environment or not.

    Parameters
    ----------
    data : GTData
        The GTData object that contains all the information about the table.

    Returns
    -------
    str
        The LaTeX code that signifies the start of the table.
    
great_tables/_utils_render_latex.py