The historical orthography is found in most Japanese dictionaries, such as Kōjien. In the current edition of the Kōjien, if the historical orthography is different from the modern spelling, the old spelling is printed in tiny katakana between the modern kana and kanji transcriptions of the word. Ellipses are used to save space when the historical and modern spellings are identical. Older editions of the Kōjien gave priority to the historical orthography.
The historical orthography should not be confused with hentaigana, alternate kana that were declared obsolete with the orthographic reforms of 1900.
In historical kana usage:
Most of the historical kana usage has been found to accurately represent certain aspects of the way words sounded during the Heian period. As the spoken language has continued to develop, some orthography looks odd to the modern eye. As these peculiarities follow fairly regular patterns, they are not difficult to learn. However, some of the historical kana usages are simply mistakes. For example,
Those familiar with Japanese writing may notice that most of the differences apply to words which are usually written in Kanji anyway, and so would require no changes to switch from one Kana system to another (unless furigana are employed). In particular, yōon sounds occur almost exclusively in the Chinese-derived readings that are usually only seen in Kanji compounds (although not entirely; 今日 kyō "today," written けふ kefu in the old system, is a native Japanese word), and therefore do not look any different (without furigana). The relative lack of difference in appearance in practice between the two systems was a major reason the spelling reform succeeded, and also why the three grammatical particles o, e, wa continue to be written as を wo, へ he, and は ha instead of お o, え e, and わ wa; many felt that changing these exceedingly common spellings would unnecessarily confuse readers. It is also for this reason that many character dictionaries continue to include the historical spellings, since they are relevant there.