| unit | names the unit used for the measurement| Status  | Optional |  | Datatype  |  |  | Suggested values include: | - cm
 - (centimetres) 
 - mm
 - (millimetres) 
 - in
 - (inches) 
 - lines
 - lines of text
 - chars
 - (characters) characters of text
 
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  | 
| quantity | specifies the length in the units specified | 
| extent | indicates the size of the object concerned using a
      project-specific vocabulary combining quantity and units in a
      single string of words.  | Status  | Optional |  | Datatype  |  1–∞ occurrences of  separated by whitespace |  | Values  | any measurement phrase, e.g. 25 letters, 2 × 3
inches. |  <gap extent="5 words"/> <height extent="2 ft 8 in"/>  |  
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| atLeast | gives a minimum  estimated value for the  measurement. | 
| atMost | gives a maximum  estimated value for the  measurement. | 
| min | where the measurement summarizes more than one
      observation, supplies the minimum value observed. | 
| max | where the measurement summarizes more than one
      observation, supplies the maximum value observed. | 
| precision | characterizes the precision of the values specified by the
      other attributes. | 
| scope | where the measurement summarizes more than one
      observation, specifies the applicability of this measurement.| Status  | Optional |  | Datatype  |  |  | Sample values include: | - all
 - measurement applies to all instances.
 - most
 - measurement applies to most of the instances inspected.
 - range
 - measurement applies to only the specified range of instances.
 
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