what is the meaning of indented keys and bracketed keys?

Indented keys: In an indented key, the paired-couplet choices

are identified in the same way and given the same

number.

Bracketed keys: The bracketed key follows the same basic principles

of contrasting choices and choices given the

same number, letter, or symbol as an indented key.

The choices, however, are always placed on adjacent

lines, thus requiring less room on a page, and the

couplets are kept together.