ABB-pattern descriptive:
满 'full' + reduplicated
当当 (an onomatopoeic / intensifying suffix). The structure
满 +
当当 makes the adjective vivid and casual. Other ABB cousins:
满满当当 (extra emphatic, four-character),
沉甸甸 'heavy-heavy',
香喷喷 'fragrant-fragrant'. Almost always used with
的 in attributive position.
