In ClickUp, I'm missing the ability to set hierarchal relations between tags, so that I can better handle complex and fluid classification of tasks/items – something that Spaces are too rigid to do.

For exemple: In a personal task management context, someone have a task called "Learn to cook more vegan dishes". In the mental model of this person, this task is related to – and motivated by – physical health (because of nutrition needs), mental health (for avoiding the suffering of animals), partner love (because its spouse is vegan) and personal leasure (because cooking helps the person to relax).

For a faster registration of the task, for a best detailed context of it in that person's life, and for an easy findability of this task later in the future, the person wants to mark it in a flexible way that can reflect it's mental model. So, he or she categorizes the task in the following tag structures:

Health > Physical

Health > Mental

Love > Partner

Leasure > Personal

Spaces, projects and lists can't solve this need because they would force the task to be submitted to only one line of hierarchy (for exemple, demanding the person to classify it as only in the Health logic, disregarding the other important contexts). This rigidity makes it more difficult to place the task (becuse the person is forced to ponder which is "the most important" aspect of it, which takes time and effort, can change in the future, and therefore can be frustrating to classify and difficult to find).

A flexible way of "positioning" the task makes it all easier and more personalized.

And I believe task hierarchies can do that.

In Evernote, a simple version of this feature is available, if you would like to check it out.