docs: confusing gimple "Statement and operand traversals"

https://gcc.gnu.org/onlinedocs/gccint/Statement-and-operand-traversals.html

has:

tree walk_gimple_op (gimple stmt, walk_tree_fn callback_op, struct 
walk_stmt_info *wi)

but according to gimple-walk.h, the 1st arg is of type gimple*.

Moreover:

tree walk_gimple_seq (gimple_seq seq, walk_stmt_fn callback_stmt, 
walk_tree_fn callback_op, struct walk_stmt_info *wi)

This function walks all the statements in the sequence SEQ calling
walk_gimple_stmt on each one. [...] If walk_gimple_stmt returns non-
NULL, the walk is stopped and the value returned. [...]

- According to gimple-walk.h, the return value of walk_gimple_seq
   is gimple* and not tree.

- The return value of walk_gimple_stmt is of type tree, and it is
   unclear how that is mapped to the return value of walk_gimple_seq
   which is gimple*.

Johann