Dominic,
You can configure the JavaScript libraries to get the Bootstrap content assist working in javascript.
Right click on the project > select Properties > expand JavaScript > Include Path. Switch to the ‘Technologies (Tern modules)’ and enable ‘Bootstrap’. Currently there is no support for adding Boostrap CSS classes on elements.
I have filed an enhancement request for CSS content assist.
Sorry for inconvenience caused. Please let us know if you see any issues.
–Swapna
MyEclipse Support