Function params_documented_elsewhere 

pub(crate) fn params_documented_elsewhere(
    tags: &[String],
    default_page: Option<&str>,
) -> bool

Returns true when the author’s roxygen block takes its argument documentation from another block, so the generators must not add @param lines for the arguments it leaves undocumented (#1590):

• the block joins another topic (joins_author_topic: @rdname topic, @describeIn topic ...), whose own block documents the arguments. roxygen2 keeps one entry per argument name on a merged page, and a generated line such as (no documentation available) is the entry that survives, so it would replace the topic’s description (and add a second entry beside a grouped @param a,b);
• the block inherits them (inherits_params).

An argument that no block documents is still reported by R CMD check (“Undocumented arguments in Rd file”), so nothing goes missing silently. See joins_author_topic for tags and default_page.