The docs build uses an internal tool to "fix up" the output from pandoc. If there are errors in the input, the source of the error is reported as "<stdin>".

$ make docs
Building target 'docs' in configuration 'macosx-x64'
Generating JDK_API javadoc for 60 modules
<stdin>:236: bad html
<stdin>:236: bad html
<stdin>:773: bad html
<stdin>:773: bad html
Finished building target 'docs' in configuration 'macosx-x64'

It would be better if the tool indicated the actual file in error.