Validation functions

Introduction
These functions are typically used on the constraint attribute of the xf:bind element. For example, as used by Form Builder:
<xf:bind
    id="control-1-bind"
    name="control-1"
    ref="control-1"
    type="xf:decimal"
    constraint="xxf:fraction-digits(2)"/>
All these functions annotate the context instance data node (element or attribute) with:
a custom MIP of the same name
with a value set to the single parameter to the function  
xxf:excluded-dates()
[SINCE Orbeon Forms 2018.2]
xxf:excluded-dates($dates as xs:date*) as xs:boolean
Return true() if the context item converted to an xs:date is not contained in the list of dates passed as the $dates argument.
xxf:fraction-digits()
[SINCE Orbeon Forms 2016.1]
xxf:fraction-digits($digits as xs:integer?) as xs:boolean
Return true() if the context item converted to a string via the string() function contains at most the number of consecutive digits specified by $digits after the decimal point ., or if there is no decimal point. Also return true() if $digits is the empty sequence.
Note the following:
Trailing 0s are not counted.
Characters other than digits are ignored.
For example, if the context item is the string "abc123.d450f0g", the resulting consecutive digits after the decimal point considered are "45" and the number of consecutive digits after the decimal point is 2.
xxf:max-length()
[SINCE Orbeon Forms 4.10]
xxf:max-length($max as xs:integer?) as xs:boolean
Return true() if the context item converted to a string via the string() function contains at most the number of characters specified by $max. Also return true() if $max is the empty sequence.
Following XPath 2.0:
what is counted is the number of XML characters in the string (or equivalently, the number of Unicode code points). Some implementations may represent a code point above xFFFF using two 16-bit values known as a surrogate. A surrogate counts as one character, not two.
xxf:min-length()
[SINCE Orbeon Forms 4.10]
xxf:min-length($min as xs:integer?) as xs:boolean
Return true() if the context item converted to a string via the string() function contains at least the number of characters specified by $min. Also return true() if $min is the empty sequence.
Following XPath 2.0:
what is counted is the number of XML characters in the string (or equivalently, the number of Unicode code points). Some implementations may represent a code point above xFFFF using two 16-bit values known as a surrogate. A surrogate counts as one character, not two.
xxf:negative()
[SINCE Orbeon Forms 2016.1]
xxf:negative() as xs:boolean
return true() if the context item converted to a string via the string() function parses as an xs:decimal which is negative
return false() otherwise
xxf:non-negative()
[SINCE Orbeon Forms 2016.1]
xxf:non-negative() as xs:boolean
return true() if the context item converted to a string via the string() function parses as an xs:decimal which is not negative
return false() otherwise
xxf:non-positive()
[SINCE Orbeon Forms 2016.1]
xxf:non-positive() as xs:boolean
return true() if the context item converted to a string via the string() function parses as an xs:decimal which is not positive
return false() otherwise
xxf:positive()
[SINCE Orbeon Forms 2016.1]
xxf:positive() as xs:boolean
return true() if the context item converted to a string via the string() function parses as an xs:decimal which is positive
return false() otherwise
xxf:upload-max-size()
[SINCE Orbeon Forms 2017.1]
xxf:upload-max-size($bytes as xs:integer?) as xs:boolean
$bytes
non-negative value: limited upload file size
-1: unlimited upload file size
-2 or lower: ignored for the purpose of checking the upload file size
always return true(), as the validation is only used at the time of upload
xxf:upload-mediatypes()
[SINCE Orbeon Forms 2017.1]
xxf:upload-mediatypes($mediatypes as xs:string?) as xs:boolean
$mediatypes 
the value is a list of space- or comma-separated mediatype ranges
a mediatype range is one of:
*/*: all mediatypes allowed
type/*: all mediatypes with prefix type are allowed (for example image/*)
type/subtype: specific mediatype such as image/jpeg, application/atom+xml, video/mp4, etc.
always return true(), as the validation is only used at the time of upload

Model functions

Controls functions