level Hierarchical Level

Used on elements that can name a nested hierarchy (for example, <comm-ref-group> or complementary or introductory titles) to indicate the level of nesting. Such groups start at “1”, with embedded groups taking higher numbers.
OPTIONAL on many elements; click for list and usage
Value Meaning
Text, numbers, or special characters The level of this element in the hierarchy, typically a counting number such as “2”.
Restriction This is an optional attribute; there is no default.
Tagged Sample

Levels of complementary title

 <intro>2015 ASME Boiler Pressure Vessel Code</intro> 
  <main>Rules for Construction of Nuclear Facility Components</main> 
 <compl level="1">Division 1</compl>
 <compl-title-wrap level="2"> 
  <compl>Subsection NH</compl> 
  <subtitle>Class 1 Components in Elevated Temperature Service</subtitle>