A more thorough explanation:

A RUBRO AD NIGRUM

A Latin phrase meaning "from the red to the black". It refers to the transition from the title of a statute, which was often printed in red letters, to its body, which was often printed in black letters.

When reading a legal document, you might see a rubro ad nigrum. For example, the title of a law might be printed in red letters, but the actual text of the law will be printed in black letters.

Another example of a rubro ad nigrum can be found in the Bible. In some versions, the words of Jesus are printed in red letters, while the rest of the text is printed in black letters.

These examples illustrate how a rubro ad nigrum is used to distinguish between different parts of a text. By using different colors or fonts, it makes it easier for readers to identify important information and navigate through the document.