Converters (mixins)

You can define custom converters which converts properties and values into new ones. This is only supported by hard-coding into your assembly and does not interpret instructions inside your input.

Example:

using SimpleCSS;

static void Main(string[] args)
{
    string css = """
        div {
            size: 100px 400px;
        }
        """;

    string pretty = SimpleCSSCompiler.Compile(css, new SimpleCSS.CSSCompilerOptions()
    {
        Converters = new()
        {
            new CssSizeConverter()
        }
    });

    Console.WriteLine(pretty);
}

public class CssSizeConverter : CSSConverter
{
    public override bool CanConvert(string propertyName, string value)
    {
        // determines if the property should be converted
        return propertyName == "size";
    }

    public override void Convert(string? value, NameValueCollection outputDeclarations)
    {
        // get values and remove the default value
        string[] values = this.SafeSplit(value);
        value = null;

        // output the new values
        outputDeclarations.Set("width", values[0]);
        outputDeclarations.Set("height", values[1]);
    }
}

And get the converted output:

div {
    width: 100px;
    height: 400px;
}

Note: don't use string.Split() to split your values. Use the base base.SafeSplit() to split values into expressions, which it supports splitting string and expression literals.