code: @Nonnull
    public FineUploader5Validation addAcceptFile (@Nonnull final IMimeType aAcceptFile)
    {
      ValueEnforcer.notNull (aAcceptFile, "AcceptFile");
      m_aValidationAcceptFiles.add (aAcceptFile);
      return this;
    }
docs: Used by the file selection dialog. Restrict the valid file types that
  appear in the selection dialog by listing valid content-type specifiers
  here. See docs on the accept attribute of the &lt;input&gt; element
  
  @param aAcceptFile
  The MIME type to be added. May not be <code>null</code>.
  @return this for chaining