Some websites assign small max-age values (or near expiration times) to state-less resources (for example 10 minute expiration-time). Thus, browsers are allowed to cache these resources for short time periods.
HtmlSpeed extends the max-age property of these resources by auto’ versioning their file-names (appending version-codes to the file-names). HtmlSpeed sets the max-age property of these versioned resources to be one year. When the content of any versioned resource is modified, its file-name is also modified (the version-code suffix is replaced).