Final answer:
The statement regarding an ornamental, knoblike projection being a carved keystone is false. A keystone is a central, structural stone in an arch, not merely decorative. Architectural elements like antefixes serve more as decorative projections.
Step-by-step explanation:
The statement is false. An ornamental, knoblike projection is not typically referred to as a carved keystone. A keystone is the central, wedge-shaped voussoir at the apex of an arch, which is crucial for holding the arch together. This keystone is often more decorative in Gothic architecture, but it is not merely ornamental as it plays a critical structural role. The term you might be looking for regarding an ornamental projection could be an antefix, which serves a more decorative purpose and was historically used on structures to protect the ends of roof tiles and offer spiritual protection from evil.
One of the engineering marvels involving the use of a keystone can be seen in aqueducts, such as the Pont-du-Gard in Nimes, France. The use of arches and the importance of the keystone in these structures demonstrate a combination of architectural innovation and aesthetic sense. In Gothic architecture, keystones could appear at the intersection of ogives as part of ribbed vaults, but these are typically not ornamental and knoblike but rather structurally supportive and often artistically integrated into the ceiling design.