(core) Update documentation for lookup/find/prevnext for the Help Center

Summary: Documentation in https://github.com/gristlabs/grist-help/ is built using `./build-functions.sh`, and the current version (as updated and landed in https://github.com/gristlabs/grist-help/pull/368) already reflects the changes in this diff.

Test Plan: No changes to functionality, only documentation comments.

Reviewers: jarek

Reviewed By: jarek

Differential Revision: https://phab.getgrist.com/D4306

sandbox/grist/functions/prevnext.py

@@ -5,24 +5,33 @@ def PREVIOUS(rec, *, group_by=(), order_by):
   column IDs, and `order_by` allows column IDs to be prefixed with "-" to reverse sort order.
 
   For example,
-  - `PREVIOUS(rec, order_by="Date")` will return the previous record when the list of records is
-    sorted by the Date column.
-  - `PREVIOUS(rec, order_by="-Date")` will return the previous record when the list is sorted by
-    the Date column in descending order.
-  - `PREVIOUS(rec, group_by="Account", order_by="Date")` will return the previous record with the
-    same Account as `rec`, when records are filtered by the Account of `rec` and sorted by Date.
+  ```python
+  PREVIOUS(rec, order_by="Date")    # The previous record when sorted by increasing Date.
+  PREVIOUS(rec, order_by="-Date")   # The previous record when sorted by decreasing Date.
+  ```
+
+  You may use `group_by` to search for the previous record within a filtered group. For example,
+  this finds the previous record with the same Account as `rec`, when records are filtered by the
+  Account of `rec` and sorted by increasing Date:
+  ```python
+  PREVIOUS(rec, group_by="Account", order_by="Date")
+  ```
 
   When multiple records have the same `order_by` values (e.g. the same Date in the examples above),
   the order is determined by the relative position of rows in views. This is done internally by
   falling back to the special column `manualSort` and the row ID column `id`.
 
   Use `order_by=None` to find the previous record in an unsorted table (when rows may be
-  rearranged by dragging them manually). For example,
-  - `PREVIOUS(rec, order_by=None)` will return the previous record in the unsorted list of records.
+  rearranged by dragging them manually). For example:
+  ```python
+  PREVIOUS(rec, order_by=None)      # The previous record in the unsorted list of records.
+  ```
 
   You may specify multiple column IDs as a tuple, for both `group_by` and `order_by`. This can be
   used to match views sorted by multiple columns. For example:
-  - `PREVIOUS(rec, group_by=("Account", "Year"), order_by=("Date", "-Amount"))`
+  ```python
+  PREVIOUS(rec, group_by=("Account", "Year"), order_by=("Date", "-Amount"))
+  ```
   """
   return _sorted_lookup(rec, group_by=group_by, order_by=order_by)._find.previous(rec)
 
@@ -39,10 +48,10 @@ def RANK(rec, *, group_by=(), order_by, order="asc"):
   `order_by`, and grouping specified by `group_by`. See [`PREVIOUS`](#previous) for details of
   these parameters.
 
-  The `order` parameter may be "asc" (which is the default) or "desc".
+  The `order` parameter may be `"asc"` (which is the default) or `"desc"`.
 
-  When `order` is "asc" or omitted, the first record in the group in the sorted order would have
-  the rank of 1. When `order` is "desc", the last record in the sorted order would have the rank
+  When `order` is `"asc"` or omitted, the first record in the group in the sorted order would have
+  the rank of 1. When `order` is `"desc"`, the last record in the sorted order would have the rank
   of 1.
 
   If there are multiple groups, there will be multiple records with the same rank. In particular,
@@ -50,7 +59,7 @@ def RANK(rec, *, group_by=(), order_by, order="asc"):
 
   For example, `RANK(rec, group_by="Year", order_by="Score", order="desc")` will return the rank of
   the current record (`rec`) among all the records in its table for the same year, ordered by
-  score.
+  decreasing score.
   """
   return _sorted_lookup(rec, group_by=group_by, order_by=order_by)._find.rank(rec, order=order)