Set LastModified to indicate the last time the Content of the response was modified. This allows web clients to determine whether their local version of that information is up-to-date. When the HTTP request is a HEAD message, this may allow the web client and server to skip a potentially expensive transfer of information. 

The value of LastModified is specified in the local time of the machine. The HTTP response message translates this value to the date encoding used by HTTP. 

LastModified is represented using the TDateTime type. The integral part of a TDateTime value is the number of days that have passed since December 30, 1899. The fractional part of a TDateTime value is the fraction of a 24-hour day that has elapsed. 

Expires 

Date 

IfModifiedSince 

Describing the Content