221: Tag combination already used in another combination
In tagged lists which contain items with a varying numbers of tags, an item’s full tag combination may not occur as the initial part of a longer tag combination within the same list. For example, the following list is invalid, because the full tag combination <Berlin><Population>
from the second line already appeared as initial part of the tag combination <Berlin><Population><1920>
in the first line.
<Berlin><Population><1920> 3,879,409
<Berlin><Population> 3,669,491
This is also the case in your document.
Solution
Make sure that the full tag combination of each item in a tagged list does not reappear as the initial part of another item’s tag combination. One way to fix the above example is by adding a tag to the shorter item to make the tag combinations unique:
<Berlin><Population><1920> 3,879,409
<Berlin><Population><2019> 3,669,491
Another approach could be to split the list in two:
--- Historic data ---
<Berlin><Population><1920> 3,879,409
--- Current data ---
<Berlin><Population> 3,669,491