Question: In a Short Message Service (SMS) as per 3GPP specifications, what is a characteristic that distinguishes a "Regular Polygon" special shape element from other shapes in terms of its edges?
Option 1: The presence of a predefined vertex angle.
Option 2: The ability to only have a fixed number of vertices (e.g., 3, 4, 5).
Option 3: All its edges are of equal length.
Option 4: It must always have a specified angle of rotation.
Explanation: According to the specifications for special shape elements in SMS, a Regular Polygon is uniquely defined by having all its edges of equal length. This characteristic is not explicitly mentioned as a requirement or option for Stars (which are defined by vertex and reference circle parameters) or Grids (defined by distribution and dimensions). Thus, equal edge lengths are what distinguish Regular Polygons from other special shapes in this context.