This module is designed specifically to implement a mechanism which moves control of whether Wikidata values are used in an infobox from the template coder at the infobox design level to the editor at the article level. It is only intended to be used inside an infobox.

The sandbox at Module:WikidataIB/sandbox should be used for testing anything other than trivial amendments.

The module provides these calls specifically for use in infoboxes at present:

  1. getValue
    getPreferredValue - obsoleted: use getValue|rank=best instead.
    getNormalValue - obsoleted: use getValue|rank=normal instead.
  2. getCoords
  3. getQualifierValue
  4. getValueByQual
  5. getValueByLang

The obsolete call getSourcedValue has now been removed as it is redundant to getValue which can do the same job using the |onlysourced=true parameter (which is set by default).

There are also these utility calls:

  1. getLink
  2. getLabel
  3. getAT
  4. getDescription
  5. pageId
  6. formatDate
  7. checkBlacklist
  8. emptyor
  9. labelorid
  10. getLang
  11. getQid

Example form of each call:

{{#invoke:WikidataIB |getValue |<PropertyID> |name=<fieldname> |suppressfields=<list of fields which will never display> |fetchwikidata=<list of fields to fetch values from Wikidata> |onlysourced=<yes/no> |noicon=<yes/no> |df=<dmy/mdy/y> |bc=<BC/BCE> |qual=<ALL/DATES/P999> |list=<ubl/hlist/prose> |linked=<yes/no> |<local parameter>}}
{{#invoke:WikidataIB |getCoords |name=<fieldname> |suppressfields=<list of fields which will never display> |fetchwikidata=<list of fields to fetch values from Wikidata> |<local parameter>}}
{{#invoke:WikidataIB |getQualifierValue |<PropertyID> |pval=<ID of target value for the property> |qual=<qualifier ID for that target value> |name=<fieldname> |suppressfields=<list of fields which will never display> |fetchwikidata=<list of fields to fetch values from Wikidata> |onlysourced=<yes/no>}}
{{#invoke:WikidataIB |getValueByQual |<PropertyID> |qualID=<qualifier property ID to match> |qvalue=<QID of target value for the qualifier property> |name=<fieldname> |suppressfields=<list of fields which will never display> |fetchwikidata=<list of fields to fetch values from Wikidata> |onlysourced=<yes/no>}}
{{#invoke:WikidataIB |getValueByLang |<PropertyID> |lang=<language code to match> |name=<fieldname> |suppressfields=<list of fields which will never display> |fetchwikidata=<list of fields to fetch values from Wikidata> |onlysourced=<yes/no>}}

Function getValue

संपादन

Parameters to getValue

संपादन
Name Alias Function Default
(first unnamed) 1 The property-ID whose values are returned. Required.
(second unnamed) 2 A locally supplied value that, if it is not empty, will be returned in preference to the value on Wikidata. empty
qid The Q-number (entity-ID) of the entity that the property belongs to. If not supplied or empty, defaults to the associated Wikidata entry of the current page – uses mw.wikibase.getEntityIdForCurrentPage(). Item id for current page
rank [Case insensitive] When set to best, returns preferred values if present, otherwise returns normal values. When set to preferred returns preferred values. When set to normal, returns normal values. When set to deprecated returns deprecated values. Any parameter value beginning with "b" is "best"; beginning with "p" is "preferred"; beginning with "n" is "normal"; beginning with "d" is deprecated. Multiple values are allowed: "p n d" would return all ranks. "Best" overrides the other flags. Other values are ignored and if no ranks are requested, preferred and normal are returned. preferred and normal
qual The property-ID of a qualifier that is to be returned in parentheses after the property. Setting qual=ALL returns all qualifiers. Setting qual=DATES returns आरंभ वेळ (P580) and शेवट (P582) with a date separator. none
fetchwikidata fwd List of fields to fetch values from. ALL fetches all fields. A value of NONE or blank or omitting the parameter fetches no fields. none
suppressfields spf List of fields which will never display. This will even force a local value in the field not to display. none
name Name of the field. When encoding an infobox, this is the name that fetchwikidata and suppressfields will recognise. Required if fetchwikidata or suppressfields is specified (except when fetchwikidata=ALL). nil
onlysourced osd A boolean which will filter out Wikidata values that are unsourced or only sourced to Wikipedia. Values no, false and 0 are all false; anything else is true. true
df Date format: may be dmy (day before month) or mdy (month before day) or y (year alone). dmy
bc Format of the BC/BCE suffix for dates. BCE
linked A boolean that enables the link to a local page via its sitelink on Wikidata. Values no, false and 0 are all false; anything else is true. true
wdlinks wdl A boolean that enables the display of links to Wikidata when no local article exists. Values no, false and 0 are all false; anything else is true. false
unitabbr A boolean that enables unit abbreviations for common units. Values no, false and 0 are all false; anything else is true. false
maxvals Sets the maximum number of values to be returned when multiple values are available. Setting it to 1 is useful where the returned string is used within another call, e.g. image. Values 0 and empty return all values. 0 (all)
collapse Sets the maximum number of values to be returned before the content is auto-collapsed. Values 0 and empty allow all content to be displayed uncollapsed. 0 (all)
linkprefix A link prefix that is prepended to the linked value when linked. Applies only to items that have articles and to strings (e.g. url). It triggers linking of strings. Any double-quotes " are stripped out, so that spaces may be passed. empty
linkpostfix A link postfix that is appended to the linked value when linked. Applies only to items that have articles and to strings (e.g. url). It triggers linking of strings. Any double-quotes " are stripped out, so that spaces may be passed. empty
prefix A prefix that is prepended to the displayed value of strings (e.g. url). Any double-quotes " are stripped out, so that spaces may be passed. empty
postfix A postfix that is appended to the displayed value of strings (e.g. url). Any double-quotes " are stripped out, so that spaces may be passed. empty
qlinkprefix Qualifier link prefix (see linkprefix). empty
qlinkpostfix Qualifier link postfix (see linkpostfix). empty
qprefix Qualifier prefix (see prefix). empty
qpostfix Qualifier postfix (see postfix). empty
sorted A boolean which enables sorting of the values returned. Values no, false and 0 are all false; anything else is true. false
qsorted A boolean which enables sorting of the qualifier values within each item returned. Values no, false and 0 are all false; anything else is true. false
noicon A boolean which will suppress the trailing "edit at Wikidata" pen-icon. Useful for when the returned value is to be further processed. Values no, false and 0 are all false; anything else is true. false
list The name of a template that the list of multiple values is then passed through. Examples include "hlist" and "ubl". Setting it to "prose" produces something like "1, 2, 3, and 4" none
sep Customises the string that is used to separate multiple returned values. Any double-quotes " are stripped out, so that spaces may be passed. If nothing or an empty string is passed it is set to the default list separator (", " in English). ", "
qsep Customises the string that is used to separate multiple returned qualifier values. Any double-quotes " are stripped out, so that spaces may be passed. If nothing or an empty string is passed it is set to the default list separator (", " in English). ", "
format Determines whether global coordinates should be rendered as degree/minute/second or as decimal degrees. Any value beginning "dec" (case insensitive) will render as decimal. Anything else will render as DMS. dms
show Determines how global coordinates should be returned. The value "longlat" will return longitude, latitude. Any other value beginning "lon" (case insensitive) will return just longitude. Any value beginning "lat" (case insensitive) will return just latitude. When used with |noicon=true, all of these will be pure numbers in decimal degrees (signed: N and E as positive), which are intended for use in mapping templates, etc. Anything other value (or nothing) will render the usual coordinate values as DMS or decimal with "NSEW" qualifiers, etc. empty
lang Allows an unlinked value to be returned in the chosen language. Takes a standard ISO language code recognised by MediaWiki. If not supplied or blank, the local language (or set language for multi-lingual wikis) is used as normal. local language

Base parameters

संपादन
  • getValue can also take a named parameter |qid= which is the Wikidata ID for an article. This will not normally be used as omitting it defaults to the current article.
  • The property whose value is to be returned is passed in the first unnamed property and is required.
  • The second unnamed parameter, if supplied, will become the returned value and no call to Wikidata will be made.

Whitelist and blacklist

संपादन
  • The name of the field that this function is called from is passed in the named parameter |name=, which is first checked against a blacklist of fields that are never to be displayed, (i.e. the call must return nil in all circumstances). If the field is not on the blacklist, it is then checked against a whitelist. If the name of the field matches, the call will return any locally supplied value if it is supplied as the second unnamed parameter, or the Wikidata value otherwise.
  • The name is compulsory when the blacklist or whitelist is used, so the module returns nil if it is not supplied, other than when |fetchwikidata=ALL.
  • The blacklist is passed in the named parameter |suppressfields=
  • The whitelist is passed in the named parameter |fetchwikidata=

The getValue function will accept a boolean parameter onlysourced which will suppress return of Wikidata values that are unsourced or only sourced to Wikipedia. The absence of the parameter, an empty parameter (|onlysourced=) and the empty string ("") all default to true (i.e. only referenced values are returned). The values no, false and 0 are treated as false (i.e. all values are returned); any other value is true (although |onlysourced=yes/no is recommended for readability).

संपादन

The getValue function will accept a boolean parameter noicon which will suppress the trailing "edit at Wikidata" icon and link for cases when the returned value is to be further processed by the infobox (e.g. a url). The absence of the parameter or an empty parameter (|noicon=) default to false (i.e. the icon is added). The empty string ("") and the values no, false and 0 are treated as false; any other value is true (although |noicon=true is recommended for readability).

In order to handle the requirement for dates in mdy, dmy or just year formats, getValue accepts a named parameter |df= that may take the values "dmy", "mdy", or "y" - default is "dmy".

As an article may require either of suffixes BC and BCE, getValue accepts a named parameter |bc= that may take the values "BC", or "BCE" - default is "BCE". Some test cases are shown at en:Module talk:WikidataIB/testing #Calls to getValue for dates.

The |rank= parameter, when set to preferred, returns only preferred values; when set to normal, returns only normal values; when set to deprecated, returns only deprecated values. If the parameter is set to best, it returns preferred values if present, otherwise normal values. Any parameter value beginning with "p" is "preferred"; any parameter value beginning with "n" is "normal"; any parameter value beginning with "d" is "deprecated"; any parameter value beginning with "b" is "best". Combinations of values are allowed, e.g. |rank=p n returns all the preferred and normal values (which is the default), although "best" overrides any other parameters.

Specific value-type handlers

संपादन

The module has specific handlers for the following data types:

  1. Items that correspond to an article in some Wikipedia, called "wikibase-items". These will be linked to the corresponding (and disambiguated) article on English Wikipedia where possible.
  2. Items that represent dates. These may be centuries, years, years and months, or years, months and days.
  3. Items that represent Commons media, urls, external ids, or other sorts of plain text.
  4. Items that represent quantities. All of these may have an associated unit, or be dimensionless, and may have a range.
  5. Items that represent global coordinates. These will be in degrees of latitude and longitude and will have an associated precision.

Items that represent other types of data are not handled at present.

The third class of data types may be used with the parameters:

  • |prefix=, |postfix=, |linkprefix=, |linkpostfix=

If you don't supply at least one of |linkprefix= or |linkpostfix=, then just |prefix= and |postfix= are used. For example, when getting the Minor Planet Center observatory code (P717) in Vienna Observatory (Q532127):

  • {{#invoke:WikidataIB|getValue|P717|fetchwikidata=ALL|onlysourced=no |prefix="before " |postfix=" after" |qid=Q532127}} → before 045 after  

Use double-quotes to enclose the parameter value if it has leading or trailing spaces (otherwise they are stripped out). If you supply |linkprefix= or |linkpostfix=, then all four parameters are used and a link is made for each value like this:

  • [[ linkprefix WikidataValue1 linkpostfix | prefix WikidataValue1 postfix]], [[ linkprefix WikidataValue2 linkpostfix | prefix WikidataValue2 postfix]], etc.

That allows multiple links to be made to different sections of a list article, such as en:List of observatory codes. For example, when getting the Minor Planet Center observatory code (P717) in Vienna Observatory (Q532127) we can make the links:

  • {{#invoke:WikidataIB|getValue|P717|fetchwikidata=ALL|onlysourced=no |prefix= |postfix= |linkprefix="List of observatory codes#" |linkpostfix= |qid=Q532127}} → [List of observatory codes#045 045]  

The parameters |prefix=, |postfix=, |linkprefix=, |linkpostfix= are also applied to wikibase-items if they are linked.

Formatting multiple returned values

संपादन
  • |sorted=<yes|no> is a boolean passed to enable sorting of the values returned. No parameter, or an empty string, or "false", or "no", or "0" disables sorting. It's only a very dumb alphabetical sort and sorts linked values as "[[ ..."
  • |sep=<separator characters> allows the separator between multiple returned values to be defined. The default is ", " (comma plus normal space). If the separator has leading or trailing spaces, enclose it in double quotes (e.g. |sep=" - "). Any double quotes are stripped from the separator. The pipe character (|) must be escaped as {{!}}. For reasons of accessibility (see en:MOS:PLIST), do not use |sep=<br> for vertical unbulleted lists; use |list=ubl instead.
  • |list=<hlist|ubl> allows multiple returned values to be displayed as a horizontal list (|list=hlist), or a vertical unbulleted list (|list=ubl). These override the separator and do not display the 'pen icon' linked to "Edit at Wikidata"

Limiting the returned values

संपादन

Sometimes a property is expected to have a single value, such as चित्र (P18), but may have multiple values on Wikidata. Setting |maxvals=1 will limit the number of values returned to 1. Any other value is possible and functions as expected, but zero is treated as "no limit".

A returned value that represents an article on the local wiki will be linked by default. This includes redirects, but not dab pages. Sometimes there is a need not to link that returned values and this may be accomplished by setting |linked=no.

Unit abbreviations

संपादन

When the returned value is a quantity, the name of the units in which it is expressed is appended. Infoboxes may wish to use abbreviations instead for common units. This can be done by setting |unitabbr=true.

A parameter |qual= may be supplied, which will return qualifiers of the required property, if they exist. If the value is set to a property id (P12345), then only the values of qualifiers with that property will be returned. If the value is set to |qual=ALL, then all of the qualifier values are returned. If the value is set to |qual=DATES then the आरंभ वेळ (P580) and the शेवट (P582) of the property are returned with a date separator. In each case, any qualifier values returned follow the property value, and are enclosed in parentheses. If multiple qualifier values are returned, they will be separated by commas by default, although the separator can be changed by specifying |qsep= (which may be enclosed in double-quotes, which are stripped out, so that spaces can be included). Setting the parameter |qsorted=yes will sort the returned qualifier values alphanumerically.

Short form of parameters

संपादन

Some of the longer parameters may be abbreviated to make infobox designs more compact:

  • fwd → fetchwikidata
  • osd → onlysourced
  • spf → suppressfields
  • wdl → wdlinks

Wrapper template

संपादन

The template {{wdib}} can be used as a convenient wrapper for {{#invoke:WikidataIB |getValue}}.

Other main functions

संपादन

Function getPreferredValue

संपादन

The getPreferredValue function works exactly like getValue, taking the same parameters, but if any values for a property have the preferred rank set, it will only return those values. This is now deprecated in favour of getValue|rank=best.

Function getNormalValue

संपादन

The getNormalValue function complements getPreferredValue, taking the same parameters, but if any values for a property have the normal rank set, it will only return those values. This is now deprecated in favour of getValue|rank=normal.

If a property has a mixture of preferred and normal ranks set, they can be separated by separate calls using getValue|rank=preferred (only returns preferred values) and getValue|rank=normal (only returns normal values).

Fetching the name(s) of the रचनाकार (P170) from Corisca and the Satyr (Q29016906):

  • {{#invoke:WikidataIB |getValue |P170 |fwd=ALL |qid=Q29016906 |osd=no}} → Artemisia Gentileschi, Aniella di Beltrano, Massimo Stanzione  
  • {{#invoke:WikidataIB |getValue |P170 |fwd=ALL |qid=Q29016906 |osd=no |rank=preferred}} → Artemisia Gentileschi  
  • {{#invoke:WikidataIB |getValue |P170 |fwd=ALL |qid=Q29016906 |osd=no |rank=normal}} → Aniella di Beltrano, Massimo Stanzione  
  • {{#invoke:WikidataIB |getValue |P170 |fwd=ALL |qid=Q29016906 |osd=no |rank=best}} → Artemisia Gentileschi  

Function getCoords

संपादन
  • getCoords can also take a named parameter |qid= which is the Wikidata ID for an article. This will not normally be used as omitting it defaults to the current article.
  • The first unnamed parameter, if supplied, will become the returned value and no call to Wikidata will be made.
  • The coordinates from Wikidata are parsed and passed to Template:Coord which returns the display as if it were called manually.
  • The blacklist of fields that are never to be displayed, and the whitelist are implemented in the same way as for getValue using |suppressfields= and |fetchwikidata=

Function getQualifierValue

संपादन

The getQualifierValue function is for use when we want to fetch the value of a qualifier. We need to know the property and the value of the property that the qualifier relates to. The parameters are:

  • The property ID passed in the unnamed parameter (or |1=)
  • The target value for that property in |pval=
  • The qualifier ID for that target value in |qual=
  • The same parameters to implement whitelisting and blacklisting of the property as in getValue
  • Optional boolean to specify whether only sourced values of the property are returned (defaults to "no") in |onlysourced=
  • Optional item ID for arbitrary access in |qid=
  • The same parameters to format output as in getValue

Example of getQualifierValue

संपादन

In South Pole Telescope (Q1513315) there is a property महत्वाची घटना (P793), which has a value बांधकाम (Q385378). That has two qualifiers, आरंभ वेळ (P580) and शेवट (P582). To get the start date:

  • {{#invoke:WikidataIB |getQualifierValue |P793 |pval=Q385378 |qual=P580 |name=xyz |fetchwikidata=ALL }}

In South Pole Telescope it returns:

  • नोव्हेंबर, इ.स. २००६  

Function getValueByQual

संपादन

The getValueByQual function returns the value of a property which has a qualifier with a given entity value. The parameters are:

  • The property ID passed in the unnamed parameter (or |1=)
  • The property ID for a qualifier (or "ALL" or "DATES") in |qualID=
  • The Wikibase-entity ID of a value for that qualifier in |qvalue=
  • The same parameters to implement whitelisting and blacklisting of the property as in getValue
  • Optional boolean to specify whether only sourced values of the property are returned (defaults to "no") in |onlysourced=
  • Optional item ID for arbitrary access in |qid=
  • The same parameters to format output as in getValue

Example of getValueByQual

संपादन

In meat (Q10990) there is a property उच्चारणाचा श्राव्य (P443) that has multiple values, each of which has a qualifier वापरलेली भाषा (P407). We can return the property value whose qualifier has the value British English (Q7979)

  • {{#invoke:WikidataIB |getValueByQual |qid=Q10990 |P443 |qualID=P407 |qvalue=Q7979 |fwd=ALL |osd=no |noicon=true}}

Function getValueByLang

संपादन

The getValueByLang function returns the value of a property which has a qualifier वापरलेली भाषा (P407) whose value has the given language code. The parameters are:

  • The property ID passed in the unnamed parameter (or |1=)
  • The MediaWiki language code to match the language whose code is given by |lang=xx[-yy]. If no code is supplied, it uses the default language.
  • The same parameters to implement whitelisting and blacklisting of the property as in getValue
  • Optional boolean to specify whether only sourced values of the property are returned (defaults to "no") in |onlysourced=
  • Optional item ID for arbitrary access in |qid=
  • The same parameters to format output as in getValue

Utility functions

संपादन
संपादन

getLink has the qid of a Wikidata entity passed as the first unnamed parameter or as |qid=

If there is a sitelink to an article on the local Wiki, it returns a link to the article with the Wikidata label as the displayed text. If there is no sitelink, it returns the label as plain text. If there is no label in the local language, it displays the qid instead.

Wikidata: Corisca and the Satyr (Q29016906) and पुरातत्त्वज्ञ (Q3621491)

Function getLabel

संपादन

getLabel has the qid of a Wikidata entity passed as the first unnamed parameter or as |qid=

It returns the Wikidata label for the local language as plain text. If there is no label in the local language, it displays the qid instead. Note that this is the label given to the Wikidata entry in the same language as the current Wiki, if the label exists.

Wikidata: Corisca and the Satyr (Q29016906) and पुरातत्त्वज्ञ (Q3621491)
  • {{#invoke:WikidataIB |getLabel |Q29016906}} → Corisca and the Satyr
  • {{#invoke:WikidataIB |getLabel |Q3621491}} → पुरातत्त्वज्ञ

Function getAT

संपादन

getAT has the qid of a Wikidata entity passed as the first unnamed parameter or as |qid=

If there is a sitelink to an article on the local Wiki, it returns the sitelink as plain text, i.e. the article title. If there is no sitelink, it returns nothing. Note that this is the title of the article in the current Wikipedia, if the interlanguage link exists in the Wikidata entry.

Wikidata: Corisca and the Satyr (Q29016906) and पुरातत्त्वज्ञ (Q3621491)
  • {{#invoke:WikidataIB |getAT |Q29016906}}
  • {{#invoke:WikidataIB |getAT |Q3621491}} → पुरातत्त्वज्ञ

Function getDescription

संपादन

getDescription has the qid of a Wikidata entity passed as |qid= (it defaults to the associated qid of the current article if omitted). It has a local parameter passed as the first unnamed parameter. Any local parameter passed (other than "Wikidata" or "none") becomes the return value. It returns the article description for the Wikidata entity in plain text if the local parameter is "Wikidata". Nothing is returned if the description doesn't exist or "none" is passed as the local parameter.

Wikidata: Corisca and the Satyr (Q29016906) and पुरातत्त्वज्ञ (Q3621491)
  • {{#invoke:WikidataIB |getDescription |qid=Q29016906 |wikidata}} → painting by Artemisia Gentileschi
  • {{#invoke:WikidataIB |getDescription |qid=Q29016906 |A painting}} → A painting
  • {{#invoke:WikidataIB |getDescription |qid=Q29016906 |none}}
  • {{#invoke:WikidataIB |getDescription |qid=Q3621491 |wikidata}} → person studying human activity in the past
  • {{#invoke:WikidataIB |getDescription |qid=Q3621491 |A profession}} → A profession
  • {{#invoke:WikidataIB |getDescription |qid=Q3621491 |none}}

Function formatDate

संपादन

formatDate accepts a datetime of the usual format from mw.wikibase.entity:formatPropertyValues, like "1 August 30 BCE" as parameter 1 and formats it according to the df (date format) and bc parameters.

  • {{#invoke:WikidataIB |formatDate | 1 August 30 BCE |bc=BCE |df=dmy}} → 1 August 30 BCE
  • {{#invoke:WikidataIB |formatDate | 1 August 30 BCE |bc=BC |df=mdy}} → August 1, 30 BC
  • df = "dmy" / "mdy" / "y" - default is "dmy"
  • bc = "BC" / "BCE" - default is "BCE"

Function checkBlacklist

संपादन

checkBlacklist allows a test to check whether a named field is allowed. It returns true if the field is not blacklisted (i.e. allowed) It returns false if the field is blacklisted (i.e. disallowed)

Example:

  • {{#if:{{#invoke:WikidataIB |checkBlacklist |name=nationality |suppressfields=residence; nationality; citizenship}} | not blacklisted | blacklisted}} → not blacklisted
  • {{#if:{{#invoke:WikidataIB |checkBlacklist |name=birth_place |suppressfields=residence; nationality; citizenship}} | not blacklisted | blacklisted}} → not blacklisted

Function emptyor

संपादन

emptyor returns nil if its first unnamed argument is just punctuation, whitespace or html tags otherwise it returns the argument unchanged (including leading/trailing space).

If the argument could contain "=", then it must be called explicitly:

  • | 1 = whatever-the-argument-is

In that case, leading and trailing spaces are trimmed.

It finds use in infoboxes where it can replace tests like:

  • {{#if: {{#invoke:WikidataIB |getvalue |P99 |fwd=ALL}} | <span class="xxx">{{#invoke:WikidataIB |getvalue |P99 |fwd=ALL}}</span> | }}

with a form that uses just a single call to Wikidata:

  • {{#invoke |WikidataIB |emptyor |1= <span class="xxx">{{#invoke:WikidataIB |getvalue |P99 |fwd=ALL}}</span> }}

Function labelorid

संपादन

labelorid is a public function to expose the output of labelOrId().

The Q-number (entity ID) is passed as |qid= or as an unnamed parameter.

It returns the Wikidata label for that entity or the qid if no label exists.

Function getLang

संपादन

getLang returns the MediaWiki language code of the current content.

If optional parameter |style=full, it returns the language name.

Function getQid

संपादन
  • getQid works with the current page and its associated Wikidata entry.
  • It returns qid, if supplied as the first unnamed parameter or as |qid=;
  • failing that, the Wikidata entity ID of the "category's main topic (P301)", if it exists;
  • failing that, the Wikidata entity ID asociated with the curent page, if it exists;
  • otherwise, nothing