Improve documentation for obsoletion (#2718)

* Improve documentation for obsoletion

Closes #2717 
Adjust numbering, indenting and newlines; add allowed values for obsolescence reason

* Apply suggestions from code review

---------

Co-authored-by: Darren A. Natale <nataled@users.noreply.github.com>

Author: Zack-83

principles/fp-019-term-stability.md

@@ -36,21 +36,22 @@ Implementation
 Detailed procedures for obsoleting a term are described on the OBO Academy page [Obsoleting an Existing Ontology Term](https://oboacademy.github.io/obook/howto/obsolete-term/). 
 
 <i><b>To obsolete a term, the ontology developer</b></i> MUST:
-1) Mark the term as obsolete
-  - OWL format: Add an "owl:deprecated" annotation property with value of "true^xsd:boolean"
-  - OBO format: Add an "is_obsolete: true" tag
-2) Prepend the string "obsolete " (including the space) to the term label <i>and</i> the `editor preferred term` (IAO:0000111), if present
-  - NOTE: To be consistent with [Principle 12](https://obofoundry.org/principles/fp-012-naming-conventions.html) "Naming Conventions", the syntax/format MUST be precisely as given above (that is, the exact string as shown, lowercase and space included, with no other punctuation before or after). Thus, the following are disallowed: "Obsolete {label}", "obsolete_{label}", "OBSOLETE {label}" (and variations thereof).
-3) Remove all existing logical axioms from the term
-4) Remove or replace all usages of the term elsewhere in the ontology. For example, if an ontology has A part-of B, and B has been deprecated with replacement by C, then the corrected axiom would be A part-of C. Likewise, if A part-of B, and B part-of C, if B is deprecated, then any part-of axiom involving B MUST be removed; that is, by stating instead A part-of C.
+1. Mark the term as obsolete:
+   - OWL format: Add an "owl:deprecated" annotation property with value of "true^xsd:boolean"
+   - OBO format: Add an "is_obsolete: true" tag
+2. Prepend the string "obsolete " (including the space) to the term label <i>and</i> the `editor preferred term` (IAO:0000111), if present
+   - NOTE: To be consistent with [Principle 12](https://obofoundry.org/principles/fp-012-naming-conventions.html) "Naming Conventions", the syntax/format MUST be precisely as given above (that is, the exact string as shown, lowercase and space included, with no other punctuation before or after). Thus, the following are disallowed: "Obsolete {label}", "obsolete_{label}", "OBSOLETE {label}" (and variations thereof).
+3. Remove all existing logical axioms from the term
+4. Remove or replace all usages of the term elsewhere in the ontology. For example, if an ontology has A part-of B, and B has been deprecated with replacement by C, then the corrected axiom would be A part-of C. Likewise, if A part-of B, and B part-of C, if B is deprecated, then any part-of axiom involving B MUST be removed; that is, by stating instead A part-of C.
 
 It is not necessary (and not advisable) to delete the textual definition.
 
 <i><b>To obsolete a term, the ontology developer</b></i> SHOULD:
-1) Indicate any exact term replacement:
+
+1. Indicate any exact term replacement:
    -  OWL: Use the `term replaced by` annotation property from OMO ([IAO:0100001](http://purl.obolibrary.org/obo/IAO_0100001)) with the value set to the IRI of the relevant term
    -  OBO: Use the `replaced_by:` tag with the value set to the CURIE of the relevant term
-2) Indicate any inexact term replacements:
+2. Indicate any inexact term replacements:
    -  OWL: Use the `oboInOwl:consider` annotation property with the value set to the full IRI(s) of the relevant term(s)
 ```
    <oboInOwl:consider rdf:resource="http://purl.obolibrary.org/obo/OBI_0001544")>
@@ -68,10 +69,10 @@ Note that some older implementations in OWL used the CURIE method as shown below
 ```
 <i><b>To obsolete a term, the ontology developer</b></i> MAY:
 
-1) Prepend the string "OBSOLETE. " (this precise string, including the space) to the term definition. NOTE: This MUST be implemented consistently. That is, if applied at all, it has to be applied to every obsoleted term definition.
-2) Indicate the reason(s) for obsoleting:
-  -  OWL: Use the `has obsolescence reason` annotation property from OMO ([IAO:0000231](http://purl.obolibrary.org/obo/IAO_0000231)) with the value set to the IRI of one of the individuals of the "obsolescence reason specification" term [IAO:0000225](http://purl.obolibrary.org/obo/IAO_0000225). See below for example.
-  -  OBO: Use `relationship:` with the CURIE for the annotation property (IAO:0000231) and a CURIE for the specific reason (an individual from the "obsolescence reason specification" term [IAO:0000225](http://purl.obolibrary.org/obo/IAO_0000225)). See below for example. Note that older implementations often used alternative methods (described after the examples). These methods are still valid, but are not preferred.
+1. Prepend the string "OBSOLETE. " (this precise string, including the space) to the term definition. NOTE: This MUST be implemented consistently. That is, if applied at all, it has to be applied to every obsoleted term definition.
+2. Indicate the reason(s) for obsoleting:
+   -  OWL: Use the `has obsolescence reason` annotation property from OMO ([IAO:0000231](http://purl.obolibrary.org/obo/IAO_0000231)) with the value set to the IRI of one of the individuals of the "obsolescence reason specification" term [IAO:0000225](http://purl.obolibrary.org/obo/IAO_0000225). See below for example.
+   -  OBO: Use `relationship:` with the CURIE for the annotation property (IAO:0000231) and a CURIE for the specific reason (an individual from the "obsolescence reason specification" term [IAO:0000225](http://purl.obolibrary.org/obo/IAO_0000225)). See below for example. Note that older implementations often used alternative methods (described after the examples). These methods are still valid, but are not preferred.
 
 Examples
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