TLDR: Compose heading content in natural title case, then use CSS to modify capitalization. Below, I explain why!
Before going any further, let's first define the different capitalization schemes. In this post I'm talking about natural language casing/capitalization, not code casing. Although I do love a good chat about snake_case vs. kebab-case vs. camelCase vs. PascalCase, that's for another day. As I understand it, these are the following forms of capitalization in the English language, and their corresponding CSS text-transform rules.