# Bad value “sidebar” for attribute “role” on element “span”. > Canonical HTML version: https://rocketvalidator.com/html-validation/bad-value-sidebar-for-attribute-role-on-element-span > Attribution: Rocket Validator (https://rocketvalidator.com) > License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) ARIA defines a fixed set of role values that user agents and assistive technologies understand. `sidebar` is not in that set, so `role="sidebar"` fails conformance checking and gives unreliable signals to screen readers. Using a valid role or the correct HTML element improves accessibility, ensures consistent behavior across browsers and AT, and keeps your markup standards‑compliant. Sidebars typically contain tangential or ancillary content (e.g., related links, promos, author info). The ARIA role that matches that meaning is `complementary`. In HTML, the semantic element for the same concept is `aside`, which by default maps to the `complementary` landmark in accessibility APIs. Prefer native semantics first: use `