CAD-like constraint-based modeling

Coming from the world of CAD I would really like it if constraints were available for modelling. They can be really useful when changing a design but wanting some features to be connected a certain way. The alternative way of doing this without constraints would be to scale every component independently and moving them around until thing look right.

I haven't seen in into any other program (other than point coincident contraint) and I think it would be really useful.

该 issue 未列出任何文件、测试或入口点。首先调研建模架构和现有的点重合约束支持，然后在实现之前明确哪些约束类型和设计行为属于范围；done 应由约定的约束行为和覆盖率来定义。

由索引模型根据 Issue 内容生成。