DVT VHDL IDE User Guide
Rev. 20.1.6, 2 April 2020
Some of the source files in your project might not be part of the full compilation (they are not referenced from the .dvt/default.build). For example code fragments which have not been integrated yet, or components which are part of a different build configuration than the active one (see Multiple .build Files). For convenience, all such files are called non-top files.
You can easily identify non-top files as they are missing the blue bullet decoration.
In order to provide advanced functionality when editing non-top files, DVT compiles them ad-hoc when opened, in the global scope. As a result, new problems might be reported and DVT's internal database is updated, which is reflected in the contents of views, autocomplete, design and class hierarchies etc.
When you are done editing a non-top-file and close the editor, all the content contributed by that file is removed: problem markers, types and API, etc.
Note: Verilog non-top-files are compiled as if part of a library called "non-top-files".
Note: The message of problems reported in non-top files are prefixed with an underscore. This is an indication that problems may be caused by compiling a file ad-hoc out of context.