Let's break down what's being tested in the provided JSON.

The benchmark is comparing three string methods: slice(), substr(), and substring(). These methods are used to extract a portion of a string, but they have slightly different behaviors depending on their parameters.

Here's a brief overview of each method:

• slice(start, end): Extracts a section of the string from the specified start index up to but not including the end index.
• substr(start[, length]): Extracts a portion of the string starting at the specified start index. The optional second argument specifies the number of characters to extract.
• substring(start, end): Similar to slice(), extracts a section of the string from the specified start index up to but not including the end index.

Now, let's discuss the options being compared:

1. Slice: This method is used when you want to extract a portion of the string starting at a specified index and going up to a certain length.
2. Substring: This method is similar to slice(), but it only extracts up to a specified end index, rather than including it.
3. Substr: This method extracts a portion of the string starting at the specified start index, with an optional second argument specifying the number of characters to extract.

Pros and Cons:

• Slice (and Substring):
  • Pros: More intuitive when you need to specify both a start and end index.
  • Cons: If you omit the end index or pass undefined as the length, it defaults to the string's length, which might not be what you expect. Also, if you pass a negative number for the length, it extracts from the end of the string instead of the beginning.
• Substr:
  • Pros: Allows specifying only the start index and optionally an offset (length) from that point to extract characters.
  • Cons: If you omit the second argument, it defaults to 1, which means extracting a single character. Also, if you pass a negative number for the offset, it can lead to unexpected behavior.

Considerations:

• In general, slice() is considered more flexible than substr() because it allows specifying both indices and an optional length.
• However, when only a start index is provided, substr() might be more intuitive since you're less likely to expect an offset (length) being specified.

Regarding the library or built-in functions used in this benchmark:

None of these methods rely on external libraries. They are all native JavaScript string methods that have been available since the language's early days.

If any special JavaScript features or syntax were mentioned, none are explicitly present here. However, some older versions of Internet Explorer had issues with slice() and substr(), including incorrectly handling negative lengths.

In summary, this benchmark helps compare how different browsers (specifically Chrome 96) handle the slicing and extraction of a string when only providing the start index or an offset in various methods, including slice(), substr(), and substring().