Result columns (not placeholders) can use the \"_multi_iri\", \"_multi\", and \"_multi_val\" suffixes to hold multiple concatenated values produced by group_concat:

_multi_iri — all values are URIs, separated by any whitespace (spaces, newlines, or tabs). Example: (group_concat(str(?item); separator=\" \") as ?items_multi_iri)

_multi — all values are literals, separated by newlines, with escaping. Example: (group_concat(replace(replace(?text, \"\\\\\\\\\", \"\\\\\\\\\\\\\\\\\"), \"[\\r\\n]+\", \"\\\\\\\\n\"); separator=\"\\n\") as ?texts_multi)

_multi_val — values can be a mix of URIs and literals, separated by newlines, with escaping. Each value is checked individually: URIs (matching https?://) are rendered as links, literals are rendered as text or sanitized HTML. Example: (group_concat(replace(replace(str(?val), \"\\\\\\\\\", \"\\\\\\\\\\\\\\\\\"), \"[\\r\\n]+\", \"\\\\\\\\n\"); separator=\"\\n\") as ?values_multi_val)