Because your code gets analyzed as you type, Sigasi knows the region of code that you are editing. The content assist feature (a.k.a. autocomplete) is fully aware of the context and tries to offer you only the relevant templates.
Templates are sensitive to the context of your code. If you type the word “component” inside a VHDL declarative region, Sigasi offers a template for the VHDL component declaration, based on your existing entities. If you type the same word, component in the body of an architecture, Sigasi offers a component instantiation.
Likewise, if in the architecture body can expand to an if generate statement, which is a concurrent statement. In a process, this will expand to an if-then statement, which is a sequential statement.
See also
- Why can't HDL designers live without block selection mode? (opinion)
- VHDL IEEE 1076-2008 Grammar (blog post)
- Testbench generation with Wavedrom (opinion)
- PoC - A Pile of Cores (opinion)
- Block Selection for VHDL Code Editing (screencast)