code: protected String buildBookEntityFile(final BuildData buildData) throws BuildProcessingException {
          final ContentSpec contentSpec = buildData.getContentSpec();
  
          final StringBuilder retValue = new StringBuilder();
  
          if (!buildData.getBuildOptions().getUseOldBugLinks() && buildData.getBuildOptions().getInsertBugLinks()) {
              // Add the bug link entities
              retValue.append("<!-- BUG LINK ENTITIES -->\n");
              try {
                  final BaseBugLinkStrategy bugLinkStrategy = buildData.getBugLinkStrategy();
                  final BugLinkOptions bugLinkOptions = buildData.getBugLinkOptions();
                  retValue.append(bugLinkStrategy.generateEntities(bugLinkOptions, buildData.getBuildName(), buildData.getBuildDate()));
              } catch (UnsupportedEncodingException e) {
                  throw new BuildProcessingException(e);
              } catch (BugLinkException e) {
                  throw new BuildProcessingException(e);
              } catch (final Exception ex) {
                  throw new BuildProcessingException("Failed to insert Bug Links into the DOM Document", ex);
              }
          }
  
          retValue.append("<!-- CS ENTITIES -->\n");
          final String entities = ContentSpecUtilities.generateEntitiesForContentSpec(contentSpec, buildData.getDocBookVersion(),
                  buildData.getEscapedBookTitle(), buildData.getOriginalBookTitle(), buildData.getOriginalBookProduct());
          retValue.append(entities);
  
          // Add the docbook.ent file for DocBook 5 builds
          if (buildData.getDocBookVersion() == DocBookVersion.DOCBOOK_50) {
              retValue.append("<!-- START DOCBOOK ENTITIES -->\n");
              retValue.append(docbook45Entities);
          }
  
          return retValue.toString();
      }
docs: Builds the book .ent file that is a basic requirement to build the book.
  
  @param buildData Information and data structures for the build.
  @return The book .ent file filled with content from the Content Spec.