docs: improve validation report reference

docs/framework/report.md

@@ -7,43 +7,64 @@ script:
 
 ## Validation Report
 
-All the `validate` functions return the Validation Report. It's an unified object containing information about a validation: source details, found error, etc. Let's explore a report:
+All the `validate` functions return a Validation Report. It is a unified object containing
+information about a validation run: whether the data is valid, validation statistics, top-level
+metadata errors, and task-level errors for each validated resource. Let's explore a report:
 
 ```python script tabs=Python
 from frictionless import validate
 
-report = validate('capital-invalid.csv', pick_errors=['duplicate-label'])
+report = validate("capital-invalid.csv", pick_errors=["duplicate-label"])
 print(report)
 ```
 
-As we can see, there are a lot of information; you can find its details description in "API Reference". Errors are grouped by tables; for some validation there are can be dozens of tables. Let's use the `report.flatten` function to simplify errors representation:
+The main report fields are:
+
+- `report.valid`: whether the whole validation run passed.
+- `report.stats`: aggregate counts such as tasks, errors, warnings, and elapsed seconds.
+- `report.errors`: top-level errors that are not associated with a specific validation task.
+- `report.tasks`: task reports, usually one per validated resource.
+
+Task reports contain their own `valid`, `place`, `labels`, `stats`, `warnings`, and `errors`
+properties. For example, package and inquiry validation can produce multiple tasks.
+
+Let's use the `report.flatten` function to simplify error representation:
 
 ```python script tabs=Python
 from pprint import pprint
 from frictionless import validate
 
-report = validate('capital-invalid.csv', pick_errors=['duplicate-label'])
-pprint(report.flatten(['rowNumber', 'fieldNumber', 'code', 'message']))
+report = validate("capital-invalid.csv", pick_errors=["duplicate-label"])
+pprint(report.flatten(["taskNumber", "rowNumber", "fieldNumber", "code", "message"]))
 ```
 
-In some situation, an error can't be associated with a table; then it goes to the top-level `report.errors` property:
+`flatten()` returns a list of rows using the requested property names. It includes top-level
+`report.errors` and all `report.tasks[].errors`; `taskNumber` is added for task-level errors.
+
+In some situations, an error can't be associated with a validation task; then it goes to the
+top-level `report.errors` property:
 
 ```python script tabs=Python
 from frictionless import validate
 
-report = validate('bad.json', type='schema')
+report = validate("bad.json", type="schema")
 print(report)
 ```
 
+For convenience, `report.task` is available when the report has exactly one task, and
+`report.error` is available when the report has exactly one error. Similarly, `task.error` is
+available when a task has exactly one error.
+
 ## Validation Errors
 
-The Error object is at the heart of the validation process. The Report has `report.errors` and `report.tables[].errors` properties that can contain the Error object. Let's explore it:
+The Error object is at the heart of the validation process. The Report has `report.errors` and
+`report.tasks[].errors` properties that can contain Error objects. Let's explore one:
 
 ```python script tabs=Python
 from frictionless import validate
 
-report = validate('capital-invalid.csv', pick_errors=['duplicate-label'])
-error = report.task.error # it's only available for 1 table / 1 error sitution
+report = validate("capital-invalid.csv", pick_errors=["duplicate-label"])
+error = report.error  # available only for single-error reports
 print(f'Type: "{error.type}"')
 print(f'Title: "{error.title}"')
 print(f'Tags: "{error.tags}"')
@@ -52,17 +73,30 @@ print(f'Message: "{error.message}"')
 print(f'Description: "{error.description}"')
 ```
 
-Above, we have listed universal error properties. Depending on the type of an error there can be additional ones. For example, for our `duplicate-label` error:
+Above, we have listed universal error properties. Depending on the type of error, there can be
+additional properties. For example, for our `duplicate-label` error:
 
 ```python script tabs=Python
 from frictionless import validate
 
-report = validate('capital-invalid.csv', pick_errors=['duplicate-label'])
-error = report.task.error # it's only available for 1 table / 1 error sitution
+report = validate("capital-invalid.csv", pick_errors=["duplicate-label"])
+error = report.error
 print(error)
 ```
 
-Please explore "Errors Reference" to learn about all the available errors and their properties.
+Some common location properties are:
+
+- `rowNumber`: the row where the error occurred.
+- `fieldName` / `fieldNumber`: the field where the error occurred, for field-specific errors.
+- `cells`: the full row values at the point where the row-level or cell-level error was detected.
+- `cell`: the specific cell value that failed, for cell-level errors.
+
+This means that `cells` provides row context, while `cell` points to the individual problematic
+value when the error is tied to a specific field. For example, an `extra-cell` error includes both
+the complete row in `cells` and the extra value in `cell`.
+
+Please explore the [Errors Reference](../errors/cell.html) to learn about all the available
+errors and their properties.
 
 ## Reference