Add notes on avoiding spurious introduction of labels.

Reviewed-by: iignatyev, iris

src/index.md

@@ -1039,9 +1039,11 @@ This list is intended to make it easier to identify which email list to include
 
 This table contains some frequently used JBS labels and their meaning. Please help keeping this dictionary up to date by adding your favorite labels. This table doesn’t dictate how to use labels, but rather document how they are used. That said, obviously it will help everyone if we try to follow a common standard and use similar labels in the same way across all entities that use JBS.
 
+Labels are an open namespace, which means that anyone can create new labels at any time. In order to avoid confusion, however, it's best to reuse existing labels where possible. This can be done by editing the "labels" field of a bug and entering the first few characters of the label you want to add. JIRA will pop up an autocomplete window with existing labels that match that prefix. Then choose one of the existing labels. Using the autocomplete window is preferable to typing the whole label name (even if you're a good typist) because it's easy for minor spelling errors to creep in, which can inadvertently introduce multiple labels with spurious spelling variations.
+
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 > ### Labels are case sensitive
-> When using labels in Jira gadgets (like pie charts, heat maps, and statistics tables) Jira will be case sensitive and treat e.g. OpenJDK and openjdk as two different labels. Searching however is case insensitive. This means that if you group a set of issues in a gadget based on a label, and then click one of the groups to see the list of issues, that list will contain more results than the gadget if there are usages of the label with different casing. This can be very confusing and for this reason the recommendation is to stick with the commonly used case for all labels, regardless of your personal taste for upper or lower case letters. Most labels are lower case only, but there are examples where upper case letters are used in the most common version of a label.
+> When using labels in Jira gadgets (like pie charts, heat maps, and statistics tables) Jira will be case sensitive and treat e.g. OpenJDK and openjdk as two different labels. Searching however is case insensitive. This means that if you group a set of issues in a gadget based on a label, and then click one of the groups to see the list of issues, that list will contain more results than the gadget if there are usages of the label with different casing. This can be very confusing and for this reason the recommendation is to stick with the commonly used case for all labels, regardless of your personal taste for upper or lower case letters. Most labels are lower case only, but there are examples where upper case letters are used in the most common version of a label. Use of the autocomplete popup window (described above) when adding labels will avoid inadvertent introduction of labels with differing case.
 
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