Final answer:
The question relates to pool safety standards, requiring a 2 inch line at the leading edge of a pool step, which is likely for visual clarity and to prevent accidents.
Step-by-step explanation:
The question pertains to safety standards for swimming pool design, specifically the features of a pool step. The required specification is that there shall be a 2 inch line at the leading edge of a pool step. This is likely referring to a non-slip or contrasting color line that serves to visually indicate the edge of the step, which is a crucial element for pool safety. These lines help swimmers discern the steps underwater to prevent accidents.
The context provided doesn't specify the nature of the line explicitly, but it relates to safety features that are often required in public or private pool regulations.