What does "irregular" mean in a sense of a missing okurigana letter? (上【あ】がる・上【あが】る, 明【あか】るい・明【あかる】い)


Some online dictionaries list the shorter writing as "irregular". What does
this mean exactly? Were those words used like that long ago? Is it an
abbreviation with writing? Or a slang?

Note that I'm not asking for an explanation of the difference between 上【のぼ】る
and 上【あ】がる.

Not sure how to tag this because I have no idea why this is happening.




The official [jōyō kanji
chart](http://www.bunka.go.jp/kokugo_nihongo/joho/kijun/naikaku/pdf/joyokanjihyo_20101130.pdf)
lists 上{あ}がる and 明{あか}るい. It does _not_ list 上{あが}る and 明{あかる}い. In other
words, the latter two are _not_ official ways to write these words.

Of course, people don't always follow the official recommendations, and even
today you'll find some variation in how people use okurigana, but I think
you'll find in this case that the official way is much more common.

So why are they included in the dictionary? According to [Jim Breen's EDICT
documentation](http://www.edrdg.org/jmdict/edict_doc.html) (and I assume
you're using EDICT because it's the only dictionary I'm aware of that has an
"irregular okurigana usage" tag), variants are included "to enable software to
match with variant forms". For the most part, you can ignore these―you'll come
across variations in okurigana yourself from time to time, but it's usually
obvious how to read them in context, and the two you picked out aren't
especially common.

You can read more official recommendations for okurigana usage [on the Agency
for Cultural Affairs
website](http://www.bunka.go.jp/kokugo_nihongo/joho/kijun/naikaku/okurikana/index.html),
although actual usage doesn't always follow these recommendations.




The official [jōyō kanji
chart](http://www.bunka.go.jp/kokugo_nihongo/joho/kijun/naikaku/pdf/joyokanjihyo_20101130.pdf)
lists 上{あ}がる and 明{あか}るい. It does _not_ list 上{あが}る and 明{あかる}い. In other
words, the latter two are _not_ official ways to write these words.

Of course, people don't always follow the official recommendations, and even
today you'll find some variation in how people use okurigana, but I think
you'll find in this case that the official way is much more common.

So why are they included in the dictionary? According to [Jim Breen's EDICT
documentation](http://www.edrdg.org/jmdict/edict_doc.html) (and I assume
you're using EDICT because it's the only dictionary I'm aware of that has an
"irregular okurigana usage" tag), variants are included "to enable software to
match with variant forms". For the most part, you can ignore these―you'll come
across variations in okurigana yourself from time to time, but it's usually
obvious how to read them in context, and the two you picked out aren't
especially common.

You can read more official recommendations for okurigana usage [on the Agency
for Cultural Affairs
website](http://www.bunka.go.jp/kokugo_nihongo/joho/kijun/naikaku/okurikana/index.html),
although actual usage doesn't always follow these recommendations.

