HTML is a simpler markup language than LaTeX or Texinfo, and the
predictive mode support for it is correspondingly simpler. It includes a
dictionary of HTML tags, dict-html, and dictionaries of valid
attributes for different tags, dict-html-tag. Completion is
context-sensitive: typing a ‘<’ character will start completing an
HTML tag, whereas within a tag predictive mode will complete from the
appropriate tag attribute dictionaries. With the default settings, HTML
support is enabled automatically when predictive completion mode is
turned on in an HTML buffer, via an entry in
predictive-major-mode-alist (see Major Modes).
To speed up loading of predictive mode's HTML support, a file containing information about the location of different regions within the document is saved to auto-overlays-filename located in predictive-auxiliary-file-location (see Miscellaneous Options), which by default is a .predictive/ subdirectory of the directory containing the HTML file.
It is safe to delete this file, or even the entire predictive-auxiliary-file-location directory, as long as the corresponding HTML file is not loaded in Emacs at the time. They will be recreated automatically next time the file is loaded. However, if you delete the dictionary files, you will lose all learned word weights (see Dictionary Learning).