Identifies functions that have external linkage.
This element is present when the function has external linkage. it has two mandatory attributes; name and value (see example below).
See ISO/IEC 14882:2003(E) 7.1.1 Storage class specifiers [dcl.stc] and 3.5 Program and linkage [basic.link]
Given this code:
extern void m();
Then function m would have the cxxFunctionStorageClassSpecifierExtern element:
<cxxFunctionStorageClassSpecifierExtern/>
If the mandatory attributes are present they must be set thus:
<cxxFunctionStorageClassSpecifierExtern name="extern" value="extern"/>