# X_TEST_ISLAND_SELECTOR_UNSUPPORTED

## Means

a selector is outside the island DOM's grammar

## Typical cause

`find`/`all`/`fire`/`resize`/`scroll` on a `mountIsland` handle was given a pseudo-class, a comma, a sibling combinator or an unquoted attribute value. The micro-DOM reads compounds of tag, `#id`, `.class`, `[attr]` and `[attr="value"]` joined by a space (descendant) or `>` (child), and nothing else — a selector outside that used to MATCH NOTHING, so the assertion after it failed on the wrong question; `cause` names the offset the parser stopped at

## Fix

spell the selector inside the grammar — `[data-role="scroller"] > ul > li button` — or address the element by a `data-*` attribute the island sets; a `:nth-child` or `:not()` question needs a browser test

[Testing](/error-codes#testing)