based on an earlier version of the Wolfram Language.
Because of its unified symbolic architecture, Mathematica provides powerful capabilities for creating layouts, both interactively and programmatically, and containing arbitrary expressions—not only text and formulas, but also graphics and dynamic elements.
"string" — a string containing arbitrary characters
Row — a row of elements, potentially extending over several lines
Text — render as text, in text font, etc.
Panel — display any expression in a panel
Placeholder — label a place to type