A @macro is a way to insert some dartdoc documentation that has been written somewhere else. That way you don't have duplicate docs that you have to maintain.
The string that follows @macro is the name of a template, which includes the documentation you'll insert. So in the TextField example:
/// {@macro flutter.widgets.editableText.keyboardType}
final TextInputType keyboardType;
the template name is flutter.widgets.editableText.keyboardType. If you go to the source code for EditableText, you'll find the template with it's documentation text:
/// {@template flutter.widgets.editableText.keyboardType}
/// The type of keyboard to use for editing the text.
///
/// Defaults to [TextInputType.text] if [maxLines] is one and
/// [TextInputType.multiline] otherwise.
/// {@endtemplate}
final TextInputType keyboardType;
The annotation @template starts the template and is followed by its name. @endtemplate finishes it.
When you view the documentation for EditableText.keyboardType and TextField.keyboardType, you can see they are exactly the same:
Read more in the dartdoc documentation.
