code: public boolean containsStartTag(@NotNull @FileExists @IsFile final File file, @NotNull final String tagName) {
          Contract.requireArgNotNull("file", file);
          FileExistsValidator.requireArgValid("file", file);
          IsFileValidator.requireArgValid("file", file);
          Contract.requireArgNotNull("tagName", tagName);
  
          final String xml = readFirstPartOfFile(file);
          return xml.indexOf("<" + tagName) > -1;
      }
docs: Checks if the given file contains a start tag within the first 1024 bytes.
  
  @param file
  File to check.
  @param tagName
  Name of the tag. A "&lt;" will be added to this name internally to locate the start tag.
  
  @return If the file contains the start tag TRUE else FALSE.