docs: Note that urgency ignores invalid dates now

Author: claremacrae

docs/Advanced/Urgency.md

@@ -27,6 +27,8 @@ Tasks simply sums up urgency scores of different aspects of a task:
 
 As you can tell from the table below, **due dates have the strongest influence on urgency.**
 
+Note that any invalid date values, referring to non-existent dates, are ignored.
+
 The scores are as follows:
 
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docs/Support and Help/Breaking Changes.md

@@ -43,5 +43,6 @@ These are all bug-fixes, improving the default behaviour, and recorded here for
   - [[Filters#Happens|happens]] date now ignores any invalid dates.
   - `sort by [date]` now puts invalid dates before valid dates, as action is required. See [[Sorting#How dates are sorted]].
   - `group by [date]` now puts `Invalid [date] date` as the first heading.
+  - The [[urgency]] calculation now ignores any invalid dates.
   - `task.due.category` and `task.due.fromNow` now handle invalid dates as different from future dates. See [[Task Properties#Values in TasksDate Properties|Values in TasksDate Properties]].
 - Code snippets used to change the look of the Edit and Postpone buttons must be changed, as explained in [[How to style buttons]], which gives several examples.