horizontal_line
Draws a horizontal line above the property, to separate it from what comes before.
It takes an optional hex color, with or without alpha. The default follows the editor theme – it is the color of Godot’s own category bars, so it tracks the theme you are using:
extends Node3D
@export_custom(PROPERTY_HINT_NONE, "horizontal_line")
var default: int = 0
@export_custom(PROPERTY_HINT_NONE, "horizontal_line:#e06c75")
var red: int = 0
@export_custom(PROPERTY_HINT_NONE, "horizontal_line:#98c379")
var green: int = 0
@export_custom(PROPERTY_HINT_NONE, "horizontal_line:#61afef")
var blue: int = 0
Note
The color is a literal, not an expression. Decorations are built once, when the inspector is built, so a color read from a property would be stale forever.