There are various placeholders for data field content but they all follow a basic format: [#...#], that means some placeholder codes quoted in square brackets and hash characters. It doesn't matter which font face, color or formatting you use for these placeholders. It is just important that all predefined character strings are not interrupted by any control characters like manual kerning, font styles, etc.
You can use placeholders even repeatedly in any number of text frames in the whole document, but the text frames have to be normal text frames on layout pages. This way you can e.g. easily personalize a 128 pages catalog on various pages and let Mr. Miller and Mrs. Brown believe afterwards that the catalog has only be printed for them.
The placeholders and their abilities are described as follows.