Knowing what my values are. My highest value is authenticity. I want to be honest with myself, first and foremost. Next up is consent. I want to uphold my right to choice, as well as everyone else's right to choice - this includes pointing out my own choices to myself, showing others that they have a choice, inviting them to say no at any time, being ok with saying no myself.
Being mindful that not everyone has the same values as me. This means being honest with myself (key value) about the fact that some folk are not my people and choose not to be kind/etc. (secondary value).
Being at peace with the idea that I sometimes need to turn away from those who choose to do things that are inauthentic or violate others' right to choice.
Having the tools to turn away from those people with grace and compassion, rather than anger. Recognising that I can't and shouldn't try to change others (because that violates their choices).
So I think overall it means - I know what my values are, and I live in accordance with them as much as possible. This includes sometimes opting out of contact with those who don't share my values. In order to do that, you need to like yourself, trust yourself, and not cling to other people for your self worth.
It's a good question OP because I think in general, boundaries are more complex and require quite a lot more emotional intelligence and risk-taking than may folk like to admit.