The standard RTE editor (rtehtmlarea) can populate the class list by parsing a CSS file that you set for it so all you need to do is to define ul.cmsms_timeline
in that CSS file. What the manual says:
The CSS file that contains the style definitions that should be applied to the edited contents. The selectors defined in this file will also be used in the block style and text style selection lists.
Example of the configuration:
RTE.default.contentCSS = fileadmin/template/rte.css
The setting is to be inserted to the TSconfig field in the (preferably root) page properties. You can open the WEB -> Info -> Page TSconfig -> RTE. to review all the RTE settings. Note that each database table might have its own configuration (e.g. RTE.tt_content.
) so make sure that your default setting is not overridden for a particular table.
Also note that after every change of the file you MIGHT need to open this file in your browser or clear the browser's cache. This is to make sure that your browser caches the current version of the file and thus that the RTE would use it.
Once that is set, you can simply assign the class in the RTE by selecting it from the "Block style" select box after you...
a) ...highlight all the list items.
b) ...click on ul
in Path: body » ul » li
which is displayed at the bottom of the RTE once you click on any list item.