# Standard functions
## XPath 2.0 functions
### Standard documentation
These functions are documented in [XQuery 1.0 and XPath 2.0 Functions and Operators (Second Edition)](https://www.w3.org/TR/xpath-functions/).
### Functions
Orbeon Forms supports the XPath functions from [XQuery 1.0 and XPath 2.0 Functions and Operators (Second Edition)](https://www.w3.org/TR/xpath-functions/).
Example of use:
```xpath
string-join(('cat', 'dog', 'alligator'), ', ')
```
Namespaces:
* These functions are available in the default function namespace.
* These function are also available in the XPath functions namespace (`http://www.w3.org/2005/xpath-functions`), usually associated with the `fn` prefix.
This means that it is usually not necessary to declare a namespace for these functions, nor is it necessary to use a prefix in calls to these functions.
We recommend *not prefixing* calls to the standard XPath functions.
### Constructors
Orbeon Forms supports the XPath constructors from [XQuery 1.0 and XPath 2.0 Functions and Operators (Second Edition)](https://www.w3.org/TR/xpath-functions/).
Example of use:
```xpath
xs:dateTime('2016-01-11T12:00:00Z')
```
These constructors are in the `http://www.w3.org/2001/XMLSchema` namespace, usually associated with the `xs` prefix. This means that using a prefix is required.
## XPath 3.0 functions
### Math functions
\[SINCE Orbeon Forms 2020.1]
This version doesn't yet support XPath 3.0, but it supports a subset of XPath 3.0 math functions. These functions are in the `http://www.w3.org/2005/xpath-functions/math` namespace, which maps to the `math` prefix:
* `math:log()`
* `math:sin()`
* `math:cos()`
* `math:tan()`
* `math:asin()`
* `math:acos()`
* `math:atan()`
* `math:atan2()`
* `math:log()`
* `math:exp()`
For more information, see [Trigonometric and exponential functions](https://www.w3.org/TR/xpath-functions-31/#trigonometry).
### environment-variable()
\[SINCE Orbeon Forms 2020.1]
This function returns the value of the specified environment variable. Before using this function, you'll want to set the [`oxf.xpath.environment-variable.enabled` property](/configuration/properties/general.md#oxf-xpath-environment-variable-enabled) to `true`. If that property isn't set to true, or the variable isn't defined, or the Java security doesn't allow access to environment variables, then the function returns an empty sequence.
```xpath
environment-variable('SERVICE_HOST')
```
## XForms functions
### Standard documentation
These functions are documented in XForms 2.0's [XPath Expressions Module](https://www.w3.org/community/xformsusers/wiki/XPath_Expressions_Module).
### Namespaces
* These functions are available in the default function namespace.
* These function are also available in the XForms namespace (`http://www.w3.org/2002/xforms`), usually associated with the `xf` prefix.
This means that it is usually not necessary to declare a namespace for these functions in the form, nor is it necessary to use a prefix in calls to the core XPath functions:
```xpath
valid(element)
```
For extra clarity, you can prefix calls to XForms functions. For example:
```xpath
xf:valid(element)
```
### XForms 2.0 functions
#### xf:bind()
\[SINCE Orbeon Forms 4.5]
```xpath
xf:bind($id as xs:string) as node()*
```
This function returns the sequence of nodes associated with the bind specified by the `id` parameter.
#### xf:valid()
\[SINCE Orbeon Forms 4.3]
```xpath
xf:valid() as xs:boolean
xf:valid($items as item()*) as xs:boolean
xf:valid($items as item()*, $relevant as xs:boolean) as xs:boolean
xf:valid($items as item()*, $relevant as xs:boolean, $recurse as xs:boolean) as xs:boolean
```
The `valid()` function returns the validity of XPath items, including instance data nodes.
### Boolean functions
* `xf:boolean-from-string()`
* `xf:is-card-number()`
### Number functions
* `xf:count-non-empty()`
* `xf:index()`
* `xf:power()`
* `xf:random()`
### String functions
* `xf:property()`
* This function supports extension property names in the `http://orbeon.org/oxf/xml/xforms` namespace (usually mapped to the `xxf` prefix). Any such property name will return the value of an XForms engine property. Example:
```xml
```
* NOTE: The standard XForms function returns an XPath 1.0 `string`. The Orbeon Forms implementation returns the following:
* empty sequence (if the property is not found)
* `xs:string`, `xs:integer`, `xs:boolean` or `xs:anyURI` depending on the type of the property
* `xf:digest()`
* `xf:hmac()`
### Date and time functions
*NOTE: Prefer the XPath 2.0 date and time functions when possible.*
* `xf:local-date()`
* `xf:local-dateTime()`
* `xf:now()`
* `xf:days-from-date()`
* `xf:days-to-date()`
* `xf:seconds-from-dateTime()`
* available as `xf:seconds-from-dateTime()` only
* `xf:seconds-to-dateTime()`
* `xf:seconds()`
* `xf:months()`
### Node-set functions
* `xf:instance()`
* `xf:current()`
* `xf:context()`
### Object functions
* `xf:event()`
### Unsupported and obsolete XForms 1.1 functions
The following functions from XForms 1.1 are obsolete:
* `xf:adjust-dateTime-to-timezone()`
* use the [XPath 2.0 Timezone Adjustment Functions on Dates and Time Values](https://www.w3.org/TR/xpath-functions/#timezone.functions), which offer similar functionality
* `xf:avg()`
* use the standard XPath 2.0 function instead (`avg()`)
* the XForms 1.1 version of this function is not implemented in Orbeon Forms
* `xf:choose()`
* use the native XPath 2.0 `if (...) then ... else ...` construct instead
* `xf:id()`
* use the native [XPath 2.0 `id()` function](https://www.w3.org/TR/xpath-functions/#func-id) instead
* `xf:if()`
* available as `xf:if()` only
* use the native XPath 2.0 `if (...) then ... else ...` construct instead
* `xf:min()`, `xf:max()`
* use the standard XPath 2.0 functions instead (`min()` and `max()`)
* the XForms 1.1 versions of these functions are not implemented in Orbeon Forms
## XSLT 2.0 functions
### Namespaces
These functions are available in the default function namespace.
Example:
```xpath
format-number(xs:integer(year), '0000')
```
### Functions
The following functions from XSLT 2.0 and XPath 3 are available:
* `format-dateTime()` ([external documentation](https://www.w3.org/TR/xpath-functions-31/#func-format-dateTime))
* `format-date()` ([external documentation](https://www.w3.org/TR/xpath-functions-31/#func-format-date))
* `format-time()` ([external documentation](https://www.w3.org/TR/xpath-functions-31/#func-format-time))
* `format-number()` ([external documentation](https://www.w3.org/TR/xpath-functions-31/#func-format-number))
*NOTE: Orbeon Forms, as of version 2021.1, still uses XPath 2.0. Even so, the functions above are available.*
For an example, see [Converting a date/time to a named timezone](/form-builder/formulas/formulas-examples.md#converting-a-date-time-to-a-named-timezone).
## eXforms functions
### Namespaces
These functions are available in the `http://www.exforms.org/exf/1-0` namespace, usually associated with the `exf` prefix.
### Functions
eXForms was a suggested set of extensions to XForms 1.0, grouped into different modules.
Orbeon Forms supports the `exf:mip` module, which includes the following functions:
* `exf:relevant()`
* `exf:readonly()`
* `exf:required()`
*NOTE: XPath 2.0-compatible versions of these functions will be available as part of XForms 2.0.*
Orbeon Forms also supports the following from the *sorting module*:
```xpath
exf:sort(
$sequence as item()*,
$sort-key as xs:string,
$datatype as xs:string?,
$order as xs:string?,
$case-order as xs:string?
) as item()*
```
Note that the second argument is interpreted as a string, unlike with `xxf:sort()`:
```xml
...
```
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