It was the first Heian Period dictionary to collate characters by pronunciation (in the iroha order) rather than by logographic radical (like the Tenrei Banshō Meigi) or word meaning (Wamyō Ruijushō).
The Iroha Jiruishō has a complex history (see Okimori 1996:8-11) involving editions of two, three, and ten fascicles (kan 卷 "scroll; volume").
Finally, at the start of the Kamakura Period, another anonymous editor compiled the expanded 10-fascicle edition, entitled 伊呂波字類抄 (with Iroha written 伊呂波 instead of 色葉).
The Iroha Jiruishō orthography shows that 12th-century Japanese continued to phonetically distinguish voiceless and voiced sounds, but the distinction between /zi/ and /di/, /zu/ and /du/, and /eu/ and /ou/ was being lost.
The Iroha jiruishō inventively groups entries by their first mora into 47 phonetic sections (部門) like i (伊), ro (呂), and ha (波); each subdivided into 21 semantic headings shown in the table below.