The suggestion is to change the word "system" to "codesystem" in the rule syntax:  * codes from system foo This makes sense logically, since the rule does refer to a code system. However, there are several reasons to stick with the current grammar: The corresponding element in ValueSet is "system" FHIR often refers to a "system" rather than a "codesystem" – for example, Coding.system, and in definitions, e.g. "The system the codes come from". There is a cost to modifying the grammar for existing users, although this should not be the main consideration, it tilts the scales a bit. The feel and flow of the FSH grammar – subjectively which  sounds  better. Some might like "code from codesystem" and others might like "code from system".  For these reasons, especially the first, we propose to keep the grammar as-is.