What is source code in <IDEA ROOT>/lib/src?

What is api source code in /lib/src

src_css-api.zip
src_database-openapi.zip
src_javaee-openapi.zip
src_jsf-openapi.zip
src_persistence-openapi.zip
src_tomcat.zip

It is helpful souce "src_javaee-openapi.zip" for implementing custom query language (not SQL, not jdbc) in IDEA?

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Original message URL: http://devnet.jetbrains.net/message/5280649#5280649