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.

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 equals .

[[+]]: 272741003 |Laterality| = 24028007 |Right| |

If the following values are provided to complete the slot:

182245002 |Entire upper limb| 182281004 |Entire lower limb| 244486005 |Entire eye| 1910005 |Entire ear| |

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

182245002 |Entire upper limb|: 272741003 |Laterality| = 24028007 |Right| 182281004 |Entire lower limb|: 272741003 |Laterality| = 24028007 |Right| 244486005 |Entire eye|: 272741003 |Laterality| = 24028007 |Right| 1910005 |Entire ear|: 272741003 |Laterality| = 24028007 |Right| |

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 and a refinement which uses the attribute The value of the attribute may be replaced by any valid value at a future time.

404684003 |Clinical finding|: 363698007 |Finding site| = [[+]] |

If the following value is provided to complete the slot:

53120007 |Upper limb structure| |

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

404684003 |Clinical finding|: 363698007 |Finding site| = 53120007 |Upper limb structure| |

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

53120007 |Upper limb structure|: 272741003|Laterality| = 7771000 |Left| |

then the result of processing the template would be:

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.

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 and a refinement whose value equals The attribute name in the expression may be replaced by any valid attribute concept at a future time.

404684003 |Clinical finding|: [[+]] = 80166006 |Streptococcus pyogenes| |

If the following values are provided to complete the slot:

42752001 |Due to| 255234002 |After| |

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

404684003 |Clinical finding|: 42752001 |Due to| = 80166006 |Streptococcus pyogenes| 404684003 |Clinical finding|: 255234002 |After| = 80166006 |Streptococcus pyogenes| |