internal package Foswiki::Form::FieldDefinition 
  internal package Foswiki::Form::FieldDefinition 
Base class of all field definition classes.
Type-specific classes are derived from this class to define specific
per-type behaviours. This class also provides default behaviours for when
a specific type cannot be loaded.
  ClassMethod new(%...) 
Construct a new 
FieldDefinition. Parameters are passed in a hash. See
Form.pm for how it is called. Subclasses should pass @_ on to this class.
  ObjectMethod finish() 
Break circular references.
  isEditable() -> $boolean 
Is the field type editable? Labels aren't, for example. Subclasses may need
to redefine this.
  isMultiValued() -> $boolean 
Is the field type multi-valued (i.e. does it store multiple values)?
Subclasses may need to redefine this.
  isTextMergeable() -> $boolean 
Is this field type mergeable using a conventional text merge?
  isMandatory() -> $boolean 
Is this field mandatory (required)?
  renderForEdit( $topicObject, $value ) -> ($col0html, $col1html) 
   $topicObject - the topic being edited
Render the field for editing. Returns two chunks of HTML; the
$col0html is appended to the HTML for the first column in the
form table, and the 
$col1html is used as the content of the second column.
  cssClasses(@classes) -> $classes 
Construct a list of the CSS classes for the form field. Adds additional
class specifiers related to the attributes of the field e.g mandatory.
Pass it a list of the other classnames you want on the field.
  getDefaultValue() -> $value 
Try and get a sensible default value for the field from the
values stored in the form definition. The result should be
a value string.
Some subclasses may not support the definition of defaults in
the form definition. In that case this method should return 
undef.
  renderHidden($meta) -> $html 
Render the form in 
$meta as a set of hidden fields.
  populateMetaDataFromQuery( $query, $meta, $old ) -> ($bValid, $bPresent) 
Given a CGI 
$query, a 
$meta object, and an array of 
$old field entries,
then populate the $meta with a row for this field definition, taking the
content from the query if it's there, otherwise from $old or failing that,
from the default defined for the type. Refuses to update mandatory fields
that have an empty value.
Return $bValid true if the value in $meta was updated (either from the
query or from a default in the form.
Return $bPresent true if a value was present in the query (even it was undef)
  ObjectMethod renderForDisplay($format, $attrs) → $html 
Render the field for display, under the control of $attrs.
The following vars in $format are expanded:
   $title - title of the form field
   $value - expanded to the 
protected value of the form field
The value is protected by 
Foswiki::Render::protectFormFieldValue.