#Styles

A Style is a cell's font, colours, alignment, border and number format.

def header as sheet.Style init sheet.withBorder(
    sheet.withBackground(
        sheet.withAlign(sheet.withBold(sheet.style(), true), sheet.Align.Centre),
        "FFF2CC"),
    sheet.BorderStyle.Thin);

$s = sheet.setAreaStyle($s, "A1:C1", $header);
$s = sheet.setAreaStyle($s, "B2:B99", sheet.withFormat(sheet.style(), "#,##0.00"));

style() is the default, which leaves everything to the application. Each builder returns a modified copy. Two styles that look the same are equal.

A colour that is not six hexadecimal digits throws.

#Interning

A sheet holds a table of its distinct styles and a per-cell index into it, as both file formats do:

$s = sheet.setAreaStyle($s, "A1:A1000", $header);
len($s.styles);       # 2: the default, plus the header
len($s.cellStyles);   # 1000

Use setAreaStyle for more than a few cells. setStyle copies the sheet on every call, the same cost as building a sheet with setRow; see The cell model.

Style and value are independent. Styling an empty cell gives a blank a background or border, and clearing a cell keeps its style.

#Number formats

withFormat takes the code both formats use: #,##0.00, yyyy-mm-dd, 0%, and ;-separated positive, negative, zero and text sections. asString never applies it; displayAt does:

$s = sheet.setStyle($s, "B2", sheet.withFormat(sheet.style(), "#,##0.00"));
sheet.asString(sheet.cell($s, "B2"));   # "1234.5"
sheet.displayAt($s, "B2");              # "1,234.50"

See Number formats.

Dates are the one place a format changes what is read. An XLSX date is a number whose format says it is a date, so the reader consults isDateFormat. A date cell with no style of its own still gets a date format on write, or the application would show the serial.

#Round trips

ODF stores #,##0.00 as a number:number element with two decimal places and grouping; Number formats covers the translation and what ODF cannot express. Gnumeric stores styles as rectangular regions; see Formats.

tools/validate-output.sh exports all three formats to HTML through LibreOffice and checks that the fill, bold, centring and two number formats arrived. It is why the ODS writer uses fo:font-family: style:font-name refers to a font face that must be declared separately, and LibreOffice ignored it.

#Not carried

• Per-edge borders. One weight covers all four edges, so a box survives but a single underline rule becomes a box.
• Border colours, and dashed, dotted and double rules, which read back as the nearest weight.
• Row heights, column widths, merged cells, frozen panes.
• Conditional formatting and data validation: not read, and dropped on a round trip.