Tidy validators.md

Author: stevepiercy

plone.app.dexterity/advanced/validators.md

@@ -1,122 +1,98 @@
 ---
 myst:
   html_meta:
-    "description": ""
-    "property=og:description": ""
-    "property=og:title": ""
-    "keywords": ""
+    "description": "Validators"
+    "property=og:description": "Validators"
+    "property=og:title": "Validators"
+    "keywords": "Plone, Validators, constraints, content types"
 ---
 
 # Validators
 
-**Creating custom validators for your type**
+This chapter describes how to create custom validators for your type.
 
-Many applications require some form of data entry validation. The
-simplest form of validation you get for free – the [z3c.form] library
-ensures that all data entered on Dexterity add and edit forms is valid
-for the field type.
+Many applications require some form of data entry validation.
+The simplest form of validation you get for free, the [z3c.form](https://pypi.org/project/z3c.form/) library ensures that all data entered in Dexterity add and edit forms is valid for the field type.
 
-It is also possible to set certain properties on the fields to add
-further validation (or even create your own fields with custom
-validation logic, although that is a lot less common). These properties
-are set as parameters to the field constructor when the schema interface
-is created. You should see the [zope.schema] package for details, but
-the most common constraints are:
+It is also possible to set certain properties on the fields to add further validation, or even create your own fields with custom validation logic, although that is a lot less common.
+These properties are set as parameters to the field constructor when the schema interface is created.
+You should see the [zope.schema](https://pypi.org/project/zope.schema/) package for details.
 
-`required=True/False`
+The most common constraints are:
 
+`required=True/False`
 : to make a field required or optional;
 
 `min` and `max`
-
-: used for `Int`, `Float`, `Datetime`, `Date`, and `Timedelta`
-  fields, specify the minimum and maximum (inclusive) allowed values of
-  the given type;
+: used for `Int`, `Float`, `Datetime`, `Date`, and `Timedelta` fields, specify the minimum and maximum (inclusive) allowed values of the given type.
 
 `min_length` and `max_length`
+: used for collection fields (`Tuple`, `List`, `Set`, `Frozenset`, `Dict`) and text fields (`Bytes`, `BytesLine`, `ASCII`, `ASCIILine`, `Text`, `TextLine`), set the minimum and maximum (inclusive) length of a field.
 
-: used for collection fields (`Tuple`, `List`, `Set`, `Frozenset`,
-  `Dict`) and text fields (`Bytes`, `BytesLine`, `ASCII`,
-  `ASCIILine`, `Text`, `TextLine`), set the minimum and maximum
-  (inclusive) length of a field.
 
 ## Constraints
 
-If this does not suffice, you can pass your own constraint function to a
-field. The constraint function should take a single argument: the value
-that is to be validated. This will be of the field’s type. The function
-should return a boolean `True` or `False`.
+If this does not suffice, you can pass your own constraint function to a field.
+The constraint function should take a single argument: the value that is to be validated.
+This will be the field's type.
+The function should return a boolean `True` or `False`.
 
-```
+```python
 def checkForMagic(value):
     return 'magic' in value
 ```
 
-:::{note}
-Hint: The constraint function does not have access to the context, but
-if you need to acquire a tool, you can use the
-`zope.component.hooks.getSite()` method to obtain the site root.
-:::
+```{note}
+The constraint function does not have access to the context, but if you need to acquire a tool, you can use the `zope.component.hooks.getSite()` method to obtain the site root.
+```
 
-To use the constraint, pass the function as the `constraint` argument to
-the field constructor, e.g.:
+To use the constraint, pass the function as the `constraint` argument to the field constructor, for example:
 
-```
+```python
 my_field = schema.TextLine(title=_(u"My field"), constraint=checkForMagic)
 ```
 
-Constraints are easy to write, but do not necessarily produce very
-friendly error messages. It is however possible to customise these error
-messages using [z3c.form] error view snippets. See the [z3c.form
-documentation](z3c.form) for more details.
+Constraints are easy to write, but do not necessarily produce very friendly error messages.
+It is possible to customize these error messages using `z3c.form` error view snippets.
+See the [z3c.form documentation](https://z3cform.readthedocs.io/en/latest/) for more details.
 
-## Invariants
 
-You’ll also notice that constraints only check a single field value. If
-you need to write a validator that compares multiple values, you can use
-an invariant. Invariants use exceptions to signal errors, which are
-displayed at the top of the form rather than next to a particular field.
+## Invariants
 
-To illustrate an invariant, let’s make sure that the start date of a
-`Program` is before the end date. In `program.py`, we add the following.
-Code not relevant to this example is snipped with an ellipsis (…):
+You'll also notice that constraints only check a single field value.
+If you need to write a validator that compares multiple values, you can use an invariant.
+Invariants use exceptions to signal errors, which are displayed at the top of the form rather than next to a particular field.
 
-```
-...
+To illustrate an invariant, let's make sure that the start date of a `Program` is before the end date.
+In `program.py`, we add the following.
 
+```python
 from zope.interface import invariant, Invalid
 
 class StartBeforeEnd(Invalid):
-    __doc__ = _(u"The start or end date is invalid")
+    __doc__ = _("The start or end date is invalid")
 
 class IProgram(model.Schema):
 
-    ...
-
     start = schema.Datetime(
-            title=_(u"Start date"),
-            required=False,
-        )
+        title=_("Start date"),
+        required=False,
+    )
 
     end = schema.Datetime(
-            title=_(u"End date"),
-            required=False,
-        )
-
-    ...
+        title=_("End date"),
+        required=False,
+    )
 
     @invariant
     def validateStartEnd(data):
         if data.start is not None and data.end is not None:
             if data.start > data.end:
-                raise StartBeforeEnd(_(u"The start date must be before the end date."))
-
-...
+                raise StartBeforeEnd(_("The start date must be before the end date."))
 ```
 
-## Form validators
 
-Finally, you can write more powerful validators by using the [z3c.form](http://pypi.python.org/pypi/z3c.form)
-widget validators. For details see the [z3c.form validators section](http://docs.plone.org/develop/plone/forms/z3c.form.html#validators).
+## Form validators
 
-[zope.schema]: http://pypi.python.org/pypi/zope.schema
+Finally, you can write more powerful validators by using the `z3c.form` widget validators.
+For details see [`z3c.form` validators](https://5.docs.plone.org/develop/plone/forms/z3c.form.html#validators).