Questions asking: "Multiple Text Styles via Expressions on a Single Text Layer", "How can I bold inline words via expression?" or "how do I use Essential Graphics and allow some words to be bold?" come up a lot on the forums and it's a bit tricky. While you can set the font style via expressions ( setStyle ), that applies to the whole text layer.
If you want some of the words to be bold but not others, you can try using sourceRectAtTime() to line text layers up, but that can get tricky and take longer to set up.
In the video, I take a different approach and ask the question: "if a word looks bold, but actually isn't, does it matter?" If you answer: "no", then you're in luck as I take you through the steps needed to create an FFX preset you can use whenever you have a text layer and need to control which words are bold. We'll achieve this using a text animator and a couple of slider controls.
As an added bonus, I also show how to combine text layers, animators and layer styles, to give you all the control you need.