The reference is divided in to "chapters", each of which has its own table of
contents.  Type:

    help ysh-$CHAPTER

Where $CHAPTER is one of:

    type-method
    builtin-func
    builtin-cmd
    stdlib
    front-end
    cmd-lang
    ysh-cmd
    expr-lang
    word-lang
    option
    special-var
    plugin

Example:

    help ysh-expr-lang
    help ysh-ysh-cmd    # may change
