In the Part Navigator, a Red X to the left of a feature indicates what?

A Red X next to a feature in the Part Navigator denotes that the feature has encountered a failure during its calculation or evaluation. This is an important visual indicator because it alerts the user that the feature no longer meets the necessary criteria or dependencies for successful regeneration. Often, this kind of failure can be due to changes in the geometry or parameters that the feature relies on, such as the modification or deletion of other features it depends on. By indicating a failure, the Red X suggests that the feature can be edited to address the issue, thus potentially correcting the failure and allowing the model to regenerate successfully. This functionality is crucial for maintaining the integrity of the design, as it provides the user with an opportunity to troubleshoot and fix problems directly within the modeling environment.

Other options, such as the feature being a parent or child, relate to the hierarchy of features but do not indicate status regarding successful execution, while a locked feature would signify that it cannot be edited, which does not apply here.