While doclint catches many/most HTML issues in source code, it doesn't process all files ... especially stand-alone HTML files such as found in doc-files directories.

For now, "tidy" can be used to check such HTML files, typically using "tidy -e <file>..."  tidy is a standard utility for Unix-like platforms.

Here is the current report for the JavaFX docs in JDK 10:


Tidy Report

  1778 files read
  1520 files had no errors or warnings
     1 files reported "Not all warnings/errors were shown."
    54 errors found
  1596 warnings found
     2 recommendations to use CSS

    85 % files with no errors or warnings
  0.93 average errors or warnings per file

  1248: Warning: <.*> anchor ".*" already defined
   186: Warning: trimming empty <.*>
    27: Warning: discarding unexpected <.*>
    18: Warning: missing <.*>
     8: Error: <.*> is not recognized!
     7: Warning: <.*> isn't allowed in <.*> elements
     3: Warning: <.*> lacks ".*" attribute
     2: Warning: <a> id and name attribute value mismatch
     2: Warning: inserting implicit <.*>
     1: Warning: <.*> missing '>' for end of tag
     1: Warning: missing <!DOCTYPE> declaration

Also note:

DocType Report

  1775: HTML5
     1: -//W3C//DTD HTML 4.01 Transitional//EN
     1: -//W3C//DTD XHTML 1.0 Transitional//EN

I recommend upgrading these files to HTML5, in case that triggers more warnings/errors to be found by tidy.