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The dot serves two different purposes in jq:

• A dot on its own means "the current object". Let's call this the identity dot. It can only appear at the start of an expression or subexpression, for example at the very start, or after a binary operator like the | or + or and, or inside an opening parenthesis (.
• A dot followed by a string or an identifier means "retrieve the named field of the current object". Let's call this an indexing dot. Whatever is to the left of it needs to be a complete subexpression, for example a literal value, a parenthesised expression, a function call, etc. It can't appear in any of the places the identity dot can appear.

The thing to understand is that in the square bracket operators, the dot shown in the documentation is an identity dot - it's not actually part of the operator itself. The operator is just the square brackets and their contents, and it needs to be attached to another complete expression.

In general, both square bracket operators (e.g. ["foo"] or [] or [0] or [2:5]) and object identifier indexing operators (e.g. .foo or ."foo") can be appended to another expression. Only the object identifier indexing operators can appear "bare" with no expression on the left. Since the square bracket operators can't appear bare, you will typically see them in the documentation composed after an identity dot.

These are all equivalent: