standard-module-chromes
Note that this example includes class additions because the examples are taken using mod_mainmenu. The suffix "_menu" to the div class and the "menu" class on the ul tag are not present with other modules.
Comparison of the Joomla! standard Module chromes These are the same from Joomla! 1.5 through 3.x
Style
Output
Appearance
rounded
Main Menu

none

table
Main Menu

horz
Main Menu

xhtml
Main Menu

html5
Main Menu

outline
left[outline]

Note that the Module chrome doesn't necessarily change the appearance
all that much - this depends on the CSS used in the template. For
example, the 'none' and 'horz' chromes look very similar, although
the underlying HTML code is very different.
Other notes: The horz is just the table layout, wrapped in a
table, tr, and td.
Until Joomla! 3: The software controlling these is in the file
/templates/system/html/modules.php.
Changes since Joomla! 4
- The standard chromes
horz,roundedandxhtmlhave been removed from core. - The core module chromes are controlled by
JLayoutfiles in directory/layouts/chromes/.