API Documentation
\

\O3PO_Settings

Manage the settings of the plugin.

Provide methods to set and get plugin settings fields and to create the respective admin page and menu entry. *

Summary

Methods
Properties
Constants
specify_page()
specify_section()
specify_field()
render_single_line_field()
render_multi_line_field()
render_password_field()
render_checkbox_field()
render_select_field()
render_array_as_comma_separated_list_field()
get_field_default()
get_field_defaults()
get_field_title()
specify_fake_field()
validate_doi_prefix()
validate_doi_suffix()
validate_four_digit_year()
validate_eprint()
validate_issn_or_empty()
validate_issn()
validate_email()
validate_url()
validate_array_as_comma_separated_list()
validate_two_letter_country_code()
validate_positive_integer()
validate_non_negative_euros()
checked_or_unchecked()
checked()
trim()
trim_strip_tags()
leave_unchanged()
get_field_value()
instance()
configured()
add_settings_page_to_menu()
render_settings_page()
register_settings()
render_plugin_settings()
render_journal_settings()
render_crossref_settings()
render_ads_settings()
render_clockss_settings()
render_doaj_settings()
render_arxiv_settings()
render_buffer_settings()
render_other_service_settings()
render_other_plugins_settings()
render_production_site_url_setting()
render_extended_search_and_navigation_setting()
render_search_form_on_search_page_setting()
render_custom_search_page_setting()
render_page_template_abstract_header_setting()
render_trackbacks_from_secondary_directly_into_database_setting()
render_page_template_for_publication_posts_setting()
render_cited_by_refresh_seconds_setting()
render_maintenance_mode_setting()
render_doi_prefix_setting()
render_journal_title_setting()
render_journal_subtitle_setting()
render_journal_description_setting()
render_journal_level_doi_suffix_setting()
render_eissn_setting()
render_publisher_setting()
render_publisher_street_and_number_setting()
render_publisher_zip_code_and_city_setting()
render_publisher_phone_setting()
render_secondary_journal_title_setting()
render_secondary_journal_level_doi_suffix_setting()
render_secondary_journal_eissn_setting()
render_developer_email_setting()
render_publisher_email_setting()
render_first_volume_year_setting()
render_license_name_setting()
render_license_type_setting()
render_license_version_setting()
render_license_url_setting()
render_license_explanation_setting()
render_publisher_country_setting()
render_crossref_id_setting()
render_crossref_pw_setting()
render_crossref_get_forward_links_url_setting()
render_crossref_deposite_url_setting()
render_crossref_test_deposite_url_setting()
render_crossref_email_setting()
render_crossref_archive_locations_setting()
render_crossref_crossmark_policy_page_doi_setting()
render_ads_api_search_url_setting()
render_ads_api_token_setting()
render_clockss_ftp_url_setting()
render_clockss_username_setting()
render_clockss_password_setting()
render_doaj_api_url_setting()
render_doaj_api_key_setting()
render_doaj_language_code_setting()
render_arxiv_url_abs_prefix_setting()
render_arxiv_url_pdf_prefix_setting()
render_arxiv_url_source_prefix_setting()
render_arxiv_url_trackback_prefix_setting()
render_arxiv_doi_feed_identifier_setting()
render_arxiv_paper_doi_feed_endpoint_setting()
render_arxiv_paper_doi_feed_days_setting()
render_doi_url_prefix_setting()
render_scholastica_manuscripts_url_setting()
render_scirate_url_abs_prefix_setting()
render_arxiv_vanity_url_prefix_setting()
render_orcid_url_prefix_setting()
render_fermats_library_url_prefix_setting()
render_fermats_library_about_url_setting()
render_fermats_library_email_setting()
render_mathjax_url_setting()
render_social_media_thumbnail_url_setting()
render_facebook_app_id_setting()
render_buffer_api_url_setting()
render_buffer_access_token_setting()
render_buffer_profile_ids_setting()
render_relevanssi_mime_types_to_exclude_setting()
render_relevanssi_index_pdfs_asynchronously_setting()
trim_ensure_not_empty_and_schedule_flush_rewrite_rules_if_changed()
validate_input()
get_plugin_name()
get_plugin_pretty_name()
No public properties found
No constants found
add_error()
$plugin_name
$slug
$pages
$sections
$fields
N/A
__construct()
__clone()
__sleep()
__wakeup()
configure()
specify_sections_and_fields()
$plugin_pretty_name
$version
$configured
$active_post_type_names_callback
N/A

Properties

$plugin_name

$plugin_name : string

The unique identifier of this plugin.

Type

string — The string used to uniquely identify this plugin.

$slug

$slug : string

Slug of this form.

Used for css classes when rendering the sections and fields. Used then storing/retreiving data from the database.

Type

string — Slug of the form.

$pages

$pages : array

Array of all pages of the form.

Type

array — Dictionary of all pages and their properties.

$sections

$sections : array

Array of all sections of the form.

Type

array — Dictionary of all sections and their properties.

$fields

$fields : array

Array of all field of the form.

Type

array — Dictionary of all fields and their properties.

$plugin_pretty_name

$plugin_pretty_name : string

The human readable name of this plugin.

Type

string — The human readable name of this plugin.

$version

$version : string

The current version of the plugin.

Type

string — The current version of the plugin.

$configured

$configured : string

Whether this singleton had already been configured.

Type

string — Whether this singleton had already been configured.

$active_post_type_names_callback

$active_post_type_names_callback : mixed

The callback from which to get the active post type names.

Type

mixed — The callback from which to get the active post type names.

Methods

specify_page()

specify_page(string  $id, string  $title, callable  $callback = null)

Specify a section of the form.

Keeps a record of all sections in $this->sections.

Parameters

string $id

Slug-name to identify the page.
string $title

Formatted title of the section. Shown as the heading for the section.
callable $callback

Function that echos out the any content at the top of the page (before the first section).

specify_section()

specify_section(string  $id, string  $title, callable  $callback, string  $page, callable  $summary_callback = null)

Specify a section of the form.

Keeps a record of all sections in $this->sections.

Parameters

string $id

Slug-name to identify the section. Used in the 'id' attribute of tags.
string $title

Formatted title of the section. Shown as the heading for the section.
callable $callback

Function that echos out any content at the top of the section (between heading and fields).
string $page

The slug-name of the page on which to show the section.
callable $summary_callback

Callback to call when composing the summary of this form.

specify_field()

specify_field(string  $id, string  $title, callable  $callback, string  $page, string  $section, array  $args, callable  $validation_callable, string  $default, integer  $max_length = false)

Specify a field of the form.

Keeps a record of all fields in $this->fields.

Parameters

string $id

Slug-name to identify the field. Used in the 'id' attribute of tags.
string $title

Formatted title of the field. Shown as the heading for the field.
callable $callback

Function that echos out any content at the top of the field (between heading and fields).
string $page

The slug-name of the page on which to show the field.
string $section

The slug-name of the section in which to show the field.
array $args

{ Extra arguments used when outputting the field. May be an empty array().

@type string $label_for When supplied, the label will be wrapped
                        in a `<label>` element, its `for` attribute populated
                        with this value.
@type string $class     CSS Class to be added to the `<tr>` element when the
                        field is output.

}
callable $validation_callable

Callable to use during validation of inputs. Must take a field ID and input as parameters and return a valid value for the field. Should call $this->add_error() to indicate problems.
string $default

Default value for the field.
integer $max_length

Maximum length of the value of the field.

render_single_line_field()

render_single_line_field(string  $id, string|null  $placeholder = null, string  $autocomplete = 'on', string  $style = false, string  $label = false, boolean  $esc_label = true, string  $label_style = false)

Render a standard text box type field.

Parameters

string $id

Id of the field.
string|null $placeholder

Placeholder text (default is null).
string $autocomplete

Whether to auto complete 'or' (default) or 'off.
string $style

CSS style.
string $label

HTML label.
boolean $esc_label

Whether to escape the content of label.
string $label_style

CSS style for the label.

render_multi_line_field()

render_multi_line_field(string  $id, integer  $rows = false, string  $style = false, boolean  $preview = false, string  $placeholder = false)

Render a multi line text box type field.

Parameters

string $id

Id of the field.
integer $rows

Number of rows
string $style

CSS style
boolean $preview

Whether to show a LaTeX preview below the field.
string $placeholder

Placeholder

render_password_field()

render_password_field(string  $id)

Render a password field.

Parameters

string $id

Id of the field.

render_checkbox_field()

render_checkbox_field(string  $id, string  $label = '', boolean  $esc_label = true)

Render a checkbox type field.

Parameters

string $id

Id of the field.
string $label

Label of the field.
boolean $esc_label

Whether to escape the content of $label, disable in case you want $label to contains htmls

render_select_field()

render_select_field(string  $id, array  $options, string  $onchange = false)

Render a select type field.

Parameters

string $id

Id of the field.
array $options

The options between which to select
string $onchange

The HTML onchange parameter

render_array_as_comma_separated_list_field()

render_array_as_comma_separated_list_field(string  $id, string  $placeholder = null)

Render an array as comma separated list type field.

Does not escape or otherwise handle individual fields that contain commas.

Parameters

string $id

Id of the field.
string $placeholder

Placeholder text.

get_field_default()

get_field_default(integer  $id) : string

Get the default value of a field by id.

Parameters

integer $id

Id of the field.

Returns

string —

Default value of the field

get_field_defaults()

get_field_defaults(boolean  $include_fake_fields = false)

Get the default value of all fields.

Parameters

boolean $include_fake_fields

Whether to also include fake fields in the list.

get_field_title()

get_field_title(integer  $id)

Get the title of a field by id.

Parameters

integer $id

Id of the field.

specify_fake_field()

specify_fake_field(string  $id, string  $default)

Add a fake field

Fake fields cannot be modified, but have default values that can be used to avoid hard coding values.

Parameters

string $id

Slug-name to identify the section. Used in the 'id' attribute of tags.
string $default

Default value for the field.

validate_doi_prefix()

validate_doi_prefix(string  $id, string  $input)

Clean user input to doi_prefix fields

Parameters

string $id

The field this was input to.
string $input

User input.

validate_doi_suffix()

validate_doi_suffix(string  $id, string  $input)

Clean user input to doi_suffix fields

Parameters

string $id

The field this was input to.
string $input

User input.

validate_four_digit_year()

validate_four_digit_year(string  $id, string  $input)

Clean user input to fields expecting a year.

Parameters

string $id

The field this was input to.
string $input

User input.

validate_eprint()

validate_eprint(string  $id, string  $input) : string

Clean user input to eprint fields

Parameters

string $id

The field this was input to.
string $input

User input.

Returns

string —

Valid issn or empty string.

validate_issn_or_empty()

validate_issn_or_empty(string  $id, string  $input) : string

Clean user input to issn fields

Parameters

string $id

The field this was input to.
string $input

User input.

Returns

string —

Valid issn or empty string.

validate_issn()

validate_issn(string  $id, string  $input)

Clean user input to issn fields

Parameters

string $id

The field this was input to.
string $input

User input.

validate_email()

validate_email(string  $id, string  $input)

Clean user input to email fields

Parameters

string $id

The field this was input to.
string $input

User input.

validate_url()

validate_url(string  $id, string  $input)

Clean user input to url fields

Parameters

string $id

The field this was input to.
string $input

User input.

validate_array_as_comma_separated_list()

validate_array_as_comma_separated_list(string  $id, string  $input)

Validate input to comma separated list fields.

Break a comma separated list into an array of fields.

Parameters

string $id

The field this was input to.
string $input

User input.

validate_two_letter_country_code()

validate_two_letter_country_code(string  $id, string  $input)

Validate two letter country code fields

Parameters

string $id

The field this was input to.
string $input

User input.

validate_positive_integer()

validate_positive_integer(string  $id, string  $input)

Validate positive integer fields

Parameters

string $id

The field this was input to.
string $input

User input.

validate_non_negative_euros()

validate_non_negative_euros(string  $id, string  $input)

Validate non-negative euro fields

Parameters

string $id

The field this was input to.
string $input

User input.

checked_or_unchecked()

checked_or_unchecked(string  $id, string  $input)

Restrict input to checked or unchecked fields

Parameters

string $id

The field this was input to.
string $input

User input.

checked()

checked(string  $id, string  $input)

Ensure that a check box field is checked

Parameters

string $id

The field this was input to.
string $input

User input.

trim()

trim(string  $id, string  $input)

Trim user input to field

Parameters

string $id

The field this was input to.
string $input

User input.

trim_strip_tags()

trim_strip_tags(string  $id, string  $input)

Trim user input to field

Parameters

string $id

The field this was input to.
string $input

User input.

leave_unchanged()

leave_unchanged(string  $id, string  $input)

Leave user input to field unchanged.

Parameters

string $id

The field this was input to.
string $input

User input.

get_field_value()

get_field_value(integer  $id)

Get the value of a field by id.

Parameters

integer $id

Id of the field.

instance()

instance(string  $plugin_name = null, string  $plugin_pretty_name = null, string  $version = null, callback  $active_post_type_names_callback = null) : \O3PO_Settings

Returns the settings singleton.

Also checks whether it has been configured.

Parameters

string $plugin_name

Simple name of this plugin.
string $plugin_pretty_name

Pretty name of this plugin.
string $version

Version of this plugin.
callback $active_post_type_names_callback

The callback from which to get the active post type names.

Returns

\O3PO_Settings —

The settings singleton.

configured()

configured() : boolean

Check whether this settings singleton has already been configured or not.

Returns

boolean —

Whether this settings singleton has already been configured or not.

add_settings_page_to_menu()

add_settings_page_to_menu()

Add the settings page to the admin menu.

To be added to the 'admin_menu' action.

render_settings_page()

render_settings_page()

Render the settings page.

register_settings()

register_settings()

Register all the settings.

To be added to the 'admin_init' action.

render_plugin_settings()

render_plugin_settings()

Render the head of the plugin settings page.

render_journal_settings()

render_journal_settings()

Render the head of the journal settings part.

render_crossref_settings()

render_crossref_settings()

Render the head of the crossref settings part.

render_ads_settings()

render_ads_settings()

Render the head of the ads settings part.

render_clockss_settings()

render_clockss_settings()

Render the head of the clockss settings part.

render_doaj_settings()

render_doaj_settings()

Render the head of the DOAJ settings part.

render_arxiv_settings()

render_arxiv_settings()

Render the head of the arXiv settings part.

render_buffer_settings()

render_buffer_settings()

Render the head of the Buffer.com settings part.

render_other_service_settings()

render_other_service_settings()

Render the head of the other services settings part.

render_other_plugins_settings()

render_other_plugins_settings()

Render the head of the other plugins settings part.

render_production_site_url_setting()

render_production_site_url_setting()

Render the setting for the production site url.

render_extended_search_and_navigation_setting()

render_extended_search_and_navigation_setting()

Render the setting for whether to show the extended search-based navigation on the home page.

render_search_form_on_search_page_setting()

render_search_form_on_search_page_setting()

Render the setting for whether to show a search form above the results on the search page.

render_custom_search_page_setting()

render_custom_search_page_setting()

Render the setting for whether to show the custom search page.

render_page_template_abstract_header_setting()

render_page_template_abstract_header_setting()

Render the setting for the abstract heading

render_trackbacks_from_secondary_directly_into_database_setting()

render_trackbacks_from_secondary_directly_into_database_setting()

Render the setting for whether to write trackbacks directly.

render_page_template_for_publication_posts_setting()

render_page_template_for_publication_posts_setting()

Render the setting for whether to use the page template for publications.

render_cited_by_refresh_seconds_setting()

render_cited_by_refresh_seconds_setting()

Render the cited by refresh seconds field

render_maintenance_mode_setting()

render_maintenance_mode_setting()

Render the setting to enabled maintenance mode.

render_doi_prefix_setting()

render_doi_prefix_setting()

Render the setting for the DOI prefix.

render_journal_title_setting()

render_journal_title_setting()

Render the setting for the journal title of the primary journal.

render_journal_subtitle_setting()

render_journal_subtitle_setting()

Render the setting for the subtitle of the primary journal.

render_journal_description_setting()

render_journal_description_setting()

Render the setting for the journal description.

render_journal_level_doi_suffix_setting()

render_journal_level_doi_suffix_setting()

Render the setting for the journal level DOI suffix.

render_eissn_setting()

render_eissn_setting()

Render the setting for the EISSN.

render_publisher_setting()

render_publisher_setting()

Render the setting for the publisher name.

render_publisher_street_and_number_setting()

render_publisher_street_and_number_setting()

Render the setting for the publisher street and number.

render_publisher_zip_code_and_city_setting()

render_publisher_zip_code_and_city_setting()

Render the setting for the publisher zip code and city.

render_publisher_phone_setting()

render_publisher_phone_setting()

Render the setting for the publisher phone.

render_secondary_journal_title_setting()

render_secondary_journal_title_setting()

Render the setting for the title of the secondary journal.

render_secondary_journal_level_doi_suffix_setting()

render_secondary_journal_level_doi_suffix_setting()

Render the setting for the journal level DOI suffix of the secondary journal.

render_secondary_journal_eissn_setting()

render_secondary_journal_eissn_setting()

Render the setting for the EISSN of the secondary journal.

render_developer_email_setting()

render_developer_email_setting()

Render the setting for the email of the developer.

render_publisher_email_setting()

render_publisher_email_setting()

Render the setting for the email of the publisher.

render_first_volume_year_setting()

render_first_volume_year_setting()

Render the setting for the year of the first volume.

render_license_name_setting()

render_license_name_setting()

Render the setting for the licence name.

render_license_type_setting()

render_license_type_setting()

Render the setting for the license type.

render_license_version_setting()

render_license_version_setting()

Render the setting for the license version.

render_license_url_setting()

render_license_url_setting()

Render the setting for the license URL.

render_license_explanation_setting()

render_license_explanation_setting()

Render the setting for the text appearing in the license statement.

render_publisher_country_setting()

render_publisher_country_setting()

Render the setting for the country of the publisher.

render_crossref_id_setting()

render_crossref_id_setting()

Render the setting for the CorssRef id.

render_crossref_pw_setting()

render_crossref_pw_setting()

Render the setting for the CorssRef password.

render_crossref_get_forward_links_url_setting()

render_crossref_get_forward_links_url_setting()

Render the setting for the url to query to retrieve citing articles.

render_crossref_deposite_url_setting()

render_crossref_deposite_url_setting()

Render the setting for the CrossRef deposit URL.

render_crossref_test_deposite_url_setting()

render_crossref_test_deposite_url_setting()

Render the setting for the URl of the CrossRef deposit test system.

render_crossref_email_setting()

render_crossref_email_setting()

Render the setting for the email to submit to crossref.

render_crossref_archive_locations_setting()

render_crossref_archive_locations_setting()

Render the setting for the archives the primary journal is listed in for submitting meta-data to CrossRef.

render_crossref_crossmark_policy_page_doi_setting()

render_crossref_crossmark_policy_page_doi_setting()

Render the setting for the crossmark policy page.

render_ads_api_search_url_setting()

render_ads_api_search_url_setting()

Render the setting for the ads api search URL.

render_ads_api_token_setting()

render_ads_api_token_setting()

Render the setting for the ads api token.

render_clockss_ftp_url_setting()

render_clockss_ftp_url_setting()

Render the setting for the CLOCKSS ftp url.

render_clockss_username_setting()

render_clockss_username_setting()

Render the setting for the CLOCKSS username.

render_clockss_password_setting()

render_clockss_password_setting()

Render the setting for the CLOCKSS password.

render_doaj_api_url_setting()

render_doaj_api_url_setting()

Render the setting for the URL of the DOAJ API.

render_doaj_api_key_setting()

render_doaj_api_key_setting()

Render the setting for the DOAJ api key.

render_doaj_language_code_setting()

render_doaj_language_code_setting()

Render the setting for the language code for DOAJ.

render_arxiv_url_abs_prefix_setting()

render_arxiv_url_abs_prefix_setting()

Render the setting for the arXiv abstract URL prefix.

render_arxiv_url_pdf_prefix_setting()

render_arxiv_url_pdf_prefix_setting()

Render the setting for the arXiv pdf URL prefix.

render_arxiv_url_source_prefix_setting()

render_arxiv_url_source_prefix_setting()

Render the setting for the arXiv source URL prefix.

render_arxiv_url_trackback_prefix_setting()

render_arxiv_url_trackback_prefix_setting()

Render the setting for the arXiv trackback prefix.

render_arxiv_doi_feed_identifier_setting()

render_arxiv_doi_feed_identifier_setting()

Render the setting for the DOI feed identifier for the arXiv.

render_arxiv_paper_doi_feed_endpoint_setting()

render_arxiv_paper_doi_feed_endpoint_setting()

Render the setting for the DOI feed endpoint for the arXiv.

render_arxiv_paper_doi_feed_days_setting()

render_arxiv_paper_doi_feed_days_setting()

Render the setting for the arXiv DOI feed number of days.

render_doi_url_prefix_setting()

render_doi_url_prefix_setting()

Render the setting for the CrossRef DOI resolution url prefix.

render_scholastica_manuscripts_url_setting()

render_scholastica_manuscripts_url_setting()

Render the setting for the Scholastica manuscript page setting.

render_scirate_url_abs_prefix_setting()

render_scirate_url_abs_prefix_setting()

Render the setting for the Scirate abstract URL prefix.

render_arxiv_vanity_url_prefix_setting()

render_arxiv_vanity_url_prefix_setting()

Render the setting for the arXiv vanity URL prefix.

render_orcid_url_prefix_setting()

render_orcid_url_prefix_setting()

Render the setting for the ORCID URL prefix.

render_fermats_library_url_prefix_setting()

render_fermats_library_url_prefix_setting()

Render the setting for the URL prefix of Fermat's library.

render_fermats_library_about_url_setting()

render_fermats_library_about_url_setting()

Render the setting for the about URL of Fermat's library.

render_fermats_library_email_setting()

render_fermats_library_email_setting()

Render the setting for the email of Fermt's library.

render_mathjax_url_setting()

render_mathjax_url_setting()

Render the setting for the MathJax URL.

render_social_media_thumbnail_url_setting()

render_social_media_thumbnail_url_setting()

Render the setting for the URL of the default thubnail for social media.

render_facebook_app_id_setting()

render_facebook_app_id_setting()

Render the setting for the Facebook App Id.

render_buffer_api_url_setting()

render_buffer_api_url_setting()

Render the setting for the Buffer.com api url.

render_buffer_access_token_setting()

render_buffer_access_token_setting()

Render the setting for the Buffer.com access token.

render_buffer_profile_ids_setting()

render_buffer_profile_ids_setting()

Render the setting for the Buffer.com prfile ids.

render_relevanssi_mime_types_to_exclude_setting()

render_relevanssi_mime_types_to_exclude_setting()

Render the setting for the Relevanssi mime types to exclude.

render_relevanssi_index_pdfs_asynchronously_setting()

render_relevanssi_index_pdfs_asynchronously_setting()

Render the setting for whether to index pdf asynchronously.

trim_ensure_not_empty_and_schedule_flush_rewrite_rules_if_changed()

trim_ensure_not_empty_and_schedule_flush_rewrite_rules_if_changed(string  $id, string  $input)

Trim user input to special fields connected to rewrite rules.

Ensure the rewrite rules are flushed when such setting is changed.

Parameters

string $id

The field this was input to.
string $input

User input.

validate_input()

validate_input(array  $input) : array

Validate settings.

Parameters

array $input

Array of all given input values to validate with ids as keys.

Returns

array —

Array of validated inputs.

get_plugin_name()

get_plugin_name() : string

Get the plugin_name.

Returns

string —

The name of the plugin.

get_plugin_pretty_name()

get_plugin_pretty_name()

Get the plugin_pretty_name.

add_error()

add_error(string  $setting, string  $code, string  $message, string  $type = 'error')

Record errors during input verification.

Calls through to WP's add_settings_error().

Parameters

string $setting

Slug title of the setting to which this error applies.
string $code

Slug-name to identify the error. Used as part of 'id' attribute in HTML output.
string $message

The formatted message text to display to the user (will be shown inside styled

and

tags).
string $type

Message type, controls HTML class. Possible values include 'error', 'success', 'warning', 'info'. Default value: 'error'

__construct()

__construct()

Make constructor private, so nobody can call "new Class".

__clone()

__clone()

Make clone magic method private, so nobody can clone instance.

__sleep()

__sleep()

Make sleep magic method private, so nobody can serialize instance.

__wakeup()

__wakeup()

Make wakeup magic method private, so nobody can unserialize instance.

configure()

configure(string  $plugin_name, string  $plugin_pretty_name, string  $version, callback  $active_post_type_names_callback)

Configure the settings singleton.

Parameters

string $plugin_name

Simple name of this plugin.
string $plugin_pretty_name

Pretty name of this plugin.
string $version

Version of this plugin.
callback $active_post_type_names_callback

The callback from which to get the active post type names.

specify_sections_and_fields()

specify_sections_and_fields()

Specifies plugin wide settings sections and fields.