I added a post function to a workflow transition to change the Priority field of an issue to High. This results in the following description in the list of post functions:

Type: class
Class: com.atlassian.jira.workflow.function.issue.UpdateIssueFieldFunction
Arguments:
field.name = priority
full.module.key = com.atlassian.jira.plugin.system.workflowupdate-issue-field-function
field.value = 10000

However, if I add a condition to only allow certain users in a group to execute the transition, the description changes to this (where 'ABC' is the group I selected in the condition):

Only users in group ABC can execute this transition.

Removing the condition reverts the description.