This is the official manual for the latest Org-mode release.
The HTML export back-end transforms Org's internal links (see Internal links) to equivalent HTML links in the output. The back-end similarly handles Org's automatic links created by radio targets (see Radio targets) similarly. For Org links to external files, the back-end transforms the links to relative paths.
For Org links to other .org files, the back-end automatically changes
the file extension to .html and makes file paths relative. If the
.org files have an equivalent .html version at the same
location, then the converted links should work without any further manual
intervention. However, to disable this automatic path translation, set
nil. When disabled, the
HTML export back-end substitutes the ‘id:’-based links in the HTML
output. For more about linking files when publishing to a directory,
see Publishing links.
Org files can also have special directives to the HTML export back-end. For
example, by using
#+ATTR_HTML lines to specify new format attributes
<img> tags. This example shows changing the link's
#+ATTR_HTML: :title The Org mode homepage :style color:red; [[http://orgmode.org]]