ConstraintLayout and the Attributes Pane

When you click on a widget inside a ConstraintLayout, the Attributes pane has a strange-looking control in the “Layout” category of attributes:

The chevrons inside the square indicate that the sizing rule is wrap_content for each axis. Clicking on one of the chevrons will toggle between states for that axis:

• a fixed width, indicated by a sizing bar
• 0dp, for stretching the size to the available space, indicated by a sawtooth line
• wrap_content, indicated by those chevrons