local function str_to_html(s)
  s = s:gsub("&", "&")
  s = s:gsub("<", "&#60;")
  s = s:gsub(">", "&#62;")
  s = s:gsub('"', "&#34;")
  s = s:gsub('%%', "&#37;") -- avoid unwanted substitutions
  return s
end

local function str_to_pattern(s)
  s = s:gsub("([%(%)%%%.%+%-%*%?%^%$])", "%%%1")
  return s
end

return {
  str_to_html = str_to_html,
  str_to_pattern = str_to_pattern,
}