1. Built-in CSS rules

XMLmind XML Editor has built-in CSS rules mainly used to style comments and processing instructions. These built-in rules are always implicitly loaded before the rules found in a CSS file. However, nothing prevents you from overriding any of the following built-in rules.

*::comment,
*::processing-instruction {
    display: block;
    margin: 2px;
    white-space: pre;
    text-align: left;
    font-family: monospace;
    font-style: normal;
    font-weight: normal;
    font-size: small;
}

*::comment {
    background-color: #FFFFCC;
    color: #808000;
}

*::processing-instruction {
    background-color: #CCFFCC;
    color: #008000;
}

*::processing-instruction(xxe-formula) {
    content: gadget("com.xmlmind.xmleditapp.spreadsheet.Formula");
    display: inline;
}

*:read-only {
    background-color: #E0F0F0;
}

@namespace xi url(http://www.w3.org/2001/XInclude);

xi|include,
xi\:include {
    display: tree;
}

@media print {
    *::comment,
    *::processing-instruction,
    *::processing-instruction(xxe-formula) {
        display: none;
    }

    *:read-only {
        background-color: transparent;
    }
}

In practice, this just means that you have nothing special to do to style comments, processing instructions and spreadsheet formulas (processing instruction xxe-formula).