X_TEST_ISLAND_SELECTOR_UNSUPPORTED

a selector is outside the island DOM's grammar

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

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