clarify backing field generation condition (https://github.com/JetBrains/kotlin-web-site/pull/481/)
clarify backing field generation condition (https://github.com/JetBrains/kotlin-web-site/pull/481/)

hltj/kotlin-web-site-cn,tsuijten/kotlin-web-site,hltj/kotlin-web-site-cn,hltj/kotlin-web-site-cn,tsuijten/kotlin-web-site,hltj/kotlin-web-site-cn,hltj/kotlin-web-site-cn,tsuijten/kotlin-web-site,tsuijten/kotlin-web-site,hltj/kotlin-web-site-cn