<table border="0"> no longer suppresses table borders

[leondeklerkfenetre]

Describe the bug

Since 3.2.5 , the HTML border="0" attribute on <table> is ignored. Every table is unconditionally assigned the TableGrid style, when the document does not already define it, so a table that explicitly asked for no borders renders as a full grid.

The code intended to handle this is still present in TableExpression.ComposeStyles, but it is unreachable.

This worked up to 3.2.4.

Expected behavior
When table borders is set to 0 or none I expect no borders visible in the output.
E.g. in the reproduction below I expect (taken from 3.2.4):
<w:tblBorders xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/2006/main"><w:top w:val="none" /><w:left w:val="none" /><w:bottom w:val="none" /><w:right w:val="none" /><w:insideH w:val="none" /><w:insideV w:val="none" /></w:tblBorders>

Repro

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net8.0</TargetFramework>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="HtmlToOpenXml.dll" Version="3.5.0" />
    <PackageReference Include="DocumentFormat.OpenXml" Version="3.5.1" />
  </ItemGroup>
</Project>

using System;
using System.IO;
using System.Linq;
using DocumentFormat.OpenXml;
using DocumentFormat.OpenXml.Packaging;
using DocumentFormat.OpenXml.Wordprocessing;
using HtmlToOpenXml;

class Program
{
    const string Html = @"<table border=""0""><tr><td>A1</td><td>A2</td></tr><tr><td>B1</td><td>B2</td></tr></table>";

    static void Main()
    {
        Console.WriteLine("HtmlToOpenXml " + typeof(HtmlConverter).Assembly.GetName().Version);

        using var stream = new MemoryStream();
        using var doc = WordprocessingDocument.Create(stream, WordprocessingDocumentType.Document);

        var mainPart = doc.AddMainDocumentPart();
        mainPart.Document = new Document(new Body());

        new HtmlConverter(mainPart).ParseBody(Html).GetAwaiter().GetResult();
        mainPart.Document.Save();

        var tblPr = mainPart.Document.Body.Descendants<Table>().First().GetFirstChild<TableProperties>();
        Console.WriteLine("tblStyle   : " + (tblPr.TableStyle?.Val?.Value ?? "<none>"));
        Console.WriteLine("tblBorders : " + (tblPr.TableBorders?.OuterXml ?? "<NOT EMITTED>"));

        var grid = mainPart.StyleDefinitionsPart?.Styles?.Elements<Style>()
            .FirstOrDefault(s => s.StyleId?.Value == "TableGrid");
        Console.WriteLine("TableGrid  : " + (grid?.StyleTableProperties?.TableBorders?.OuterXml ?? "<absent>"));
    }
}

[leondeklerkfenetre]

If you are interested here is a small analysis created by claude 🤖

Root cause

TableExpression.ComposeStyles (decompiled from the shipped 3.5.0 assembly):

var borders = styleAttributes.GetBorders();
if (!borders.IsEmpty)
{
    // CSS borders -> emits Top/Left/Right/Bottom only
}
else if (!borders.IsEmpty && tableNode.Border == 0)   // <-- can never be true
{
    // emits all six sides as None
}
else if (tableNode.Border >= 1)
{
    // emits the grid
}

The second branch sits inside the else of !borders.IsEmpty. Reaching it implies borders.IsEmpty == true, therefore !borders.IsEmpty is always false and the branch is dead code.

In 3.2.3 the same branch read simply:

else if (tableNode.Border == 0)

so the !borders.IsEmpty && guard appears to have been added in 3.2.5.

Suggested fix

else if (borders.IsEmpty && tableNode.Border == 0)

or drop the redundant guard entirely, restoring the pre-3.2.5 form.

Secondary observation

<table border="0" style="border:none"> takes the first branch, which emits only Top/Left/Right/Bottom and leaves insideH/insideV to the table style. Because that style is TableGrid, the inner grid lines survive even though the CSS declares no border — the table loses its outer box but keeps its inner lines.

This may be the same underlying cause as the (closed) issue #187, where border: hidden on a table still rendered visible borders. Two possible directions: have the CSS branch also emit insideH/insideV when the declared border resolves to none/hidden, or stop defaulting to a bordered table style when the HTML has not asked for borders.

Workaround for anyone else hitting this

Inject border:none into the style of the table and of every one of its cells before conversion. Cell-level tcBorders is the only direct formatting that overrides a table style's inside borders, so the table-level declaration alone is not enough.