Question

From time to time I would like to apply some custom extra syntax highlighting on the current buffer.

How can this be done using the build in vim syntax/highlight system (I do not want to use the Highlight plugin)

As example, I would like to highlight all assert statements in current buffer.

Answer 1

If the highlighting is for certain filetypes (e.g. Java) only, and you want it all the time, I’d extend the original syntax with :syn match ... definitions placed in ~/.vim/after/syntax/java.vim.

For spontaneous highlighting, use :match (or :2match), as dwalter has shown.

If you’re gonna write a more elaborate mapping, maybe with toggling on/off logic, use matchadd() / matchdelete().

Finally, if you need highlighting for arbitrary words / strings, like marking up a document with a text marker, I’d suggest the comfort of a plugin like Mark (which I have taken over maintaining).