# Simple Replacement Slots

Replacement slots serve as a placeholder for a value that is not known at the time of authoring, but which can be completed at a subsequent time using data recorded elsewhere (such as in an information model or entered into a data entry form). A slot indicates that it may be replaced by a value by including a plus sign ( + ) as the first symbol within the slot. Replacement slots may be used in an expression template wherever a concept, expression or symbol may appear within an expression.

## Focus concept

A replacement slot may be used to delay the selection of a focus concept in an expression. For example, the expression template below uses a slot to indicate that the focus concept in the expression can be replaced with any appropriate SNOMED CT expression. This expression template represents any expression with a single refinement in which the [| Laterality|](http://snomed.info/id/272741003) equals [| Right|](http://snomed.info/id/24028007) .

{% @snomed-syntax-highlighter/snomed-syntax-highlighter lines="1" content="\[\[+]]: 272741003 |Laterality| = 24028007 |Right|" %}

If the following values are provided to complete the slot:

[182245002 |Entire upper limb|](http://snomed.info/id/182245002)\
[182281004 |Entire lower limb|](http://snomed.info/id/182281004)\
[244486005 |Entire eye|](http://snomed.info/id/244486005)\
[1910005 |Entire ear|](http://snomed.info/id/1910005)

then the expressions that result from processing the template would be:

{% @snomed-syntax-highlighter/snomed-syntax-highlighter lines="1" content="182245002 |Entire upper limb| : 272741003 |Laterality| = 24028007 |Right|" processed="true" %}

{% @snomed-syntax-highlighter/snomed-syntax-highlighter lines="1" content="182281004 |Entire lower limb| : 272741003 |Laterality| = 24028007 |Right|" processed="true" %}

{% @snomed-syntax-highlighter/snomed-syntax-highlighter lines="1" content="244486005 |Entire eye| : 272741003 |Laterality| = 24028007 |Right|" processed="true" %}

{% @snomed-syntax-highlighter/snomed-syntax-highlighter lines="1" content="1910005 |Entire ear| : 272741003 |Laterality| = 24028007 |Right|" processed="true" %}

## Attribute Value

A replacement slot may also be used to replace an attribute value in an expression. For example, the expression template below represents any expression with a focus concept of [| Clinical finding|](http://snomed.info/id/404684003) and a refinement which uses the attribute [| Finding site|](http://snomed.info/id/363698007) . The value of the [| Finding site|](http://snomed.info/id/363698007) attribute may be replaced by any valid value at a future time.

{% @snomed-syntax-highlighter/snomed-syntax-highlighter lines="1" content="404684003 |Clinical finding| : 363698007 |Finding site| = \[\[+]]" %}

If the following value is provided to complete the slot:

[53120007 |Upper limb structure|](http://snomed.info/id/53120007)

then the expression that results from processing the template would be:

{% @snomed-syntax-highlighter/snomed-syntax-highlighter lines="1" content="404684003 |Clinical finding| : 363698007 |Finding site| = 53120007 |Upper limb structure|" %}

If, however, the value provided to complete the slot was the expression:

{% @snomed-syntax-highlighter/snomed-syntax-highlighter lines="1" content="53120007 |Upper limb structure| : 272741003 |Laterality| = 7771000 |Left" %}

then the result of processing the template would be:

{% @snomed-syntax-highlighter/snomed-syntax-highlighter lines="2" content="404684003 |Clinical finding| : 363698007 |Finding site| =
( 53120007 |Upper limb structure| : 272741003 |Laterality| = 7771000 |Left| )" %}

Please note that the template processor must add round brackets around the subexpression to ensure that the resulting expression is syntactically valid.

## Attribute Name

A replacement slot may also be used to replace an attribute name in an expression. For example, the expression template below represents any expression with a focus concept of [| Clinical finding|](http://snomed.info/id/404684003) and a refinement whose value equals [| Rheumatic fever|](http://snomed.info/id/58718002) The attribute name in the expression may be replaced by any valid attribute concept at a future time.

{% @snomed-syntax-highlighter/snomed-syntax-highlighter lines="1" content="404684003 |Clinical finding| : \[\[+]] = 80166006 |Streptococcus pyogenes|" %}

If the following values are provided to complete the slot:

[42752001 |Due to|](http://snomed.info/id/42752001)\
[255234002 |After|](http://snomed.info/id/255234002)

then the expressions that result from processing the template would be:

{% @snomed-syntax-highlighter/snomed-syntax-highlighter lines="1" content="404684003 |Clinical finding| : 42752001 |Due to| = 80166006 |Streptococcus pyogenes|" processed="true" %}

{% @snomed-syntax-highlighter/snomed-syntax-highlighter lines="1" content="404684003 |Clinical finding| : 255234002 |After| = 80166006 |Streptococcus pyogenes|" processed="true" %}

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