The spellCheckOptions element allows to specify spell-checker options, for example whether the on-the-fly spell-checking should be turned on by default, which elements should not be checked for spelling, etc. Excerpts from rng_section_config/common.incl (same file for all variants):

<spellCheckOptions useAutomaticSpellChecker="true" 
                   languageAttribute="xml:lang"
                   skippedElements="s:literal" />

The documentResources element allows to specify how to determine the resource files attached to the document being edited. In the case of a "Simple Section" document, the only resource files are the image files pointed to by the image elements. Excerpts from rng_section_config/common.incl (same file for all variants):

<documentResources>
  <resource path="//s:image/@source" />
</documentResources>

Knowing which resource files are attached to the document being edited is needed to implement File → Save As and also the conversion of the document being edited to other formats (see below).