TypeError: rootSection.header is not a function

No Styleguide is generated. The script stops with:

**TypeError: rootSection.header is not a function**

Using a cloned default builde template.

```
node_modules/kss/bin/kss --version
3.0.0-beta.14

node_modules/kss/bin/kss --verbose --source scss --destination styleguide --builder styleguide-template/guru-handlebars
...Parsing your style guide:

Building your KSS style guide!

* KSS Source : /Users/tho/htdocs/drupal_guru_testing/vdd/data/drupal8/themes/guru/scss
* Destination : /Users/tho/htdocs/drupal_guru_testing/vdd/data/drupal8/themes/guru/styleguide
* Builder : /Users/tho/htdocs/drupal_guru_testing/vdd/data/drupal8/themes/guru/styleguide-template/guru-handlebars

- /Users/tho/htdocs/drupal_guru_testing/vdd/data/drupal8/themes/guru/scss/abstractions/__styleguide_section.scss
- /Users/tho/htdocs/drupal_guru_testing/vdd/data/drupal8/themes/guru/scss/base/__reset.scss
- /Users/tho/htdocs/drupal_guru_testing/vdd/data/drupal8/themes/guru/scss/base/__styleguide_section.scss
- /Users/tho/htdocs/drupal_guru_testing/vdd/data/drupal8/themes/guru/scss/base/_abstract-to-concrete.generated.scss
- /Users/tho/htdocs/drupal_guru_testing/vdd/data/drupal8/themes/guru/scss/base/_customer-fonts.scss
- /Users/tho/htdocs/drupal_guru_testing/vdd/data/drupal8/themes/guru/scss/base/_form-elements.scss
- /Users/tho/htdocs/drupal_guru_testing/vdd/data/drupal8/themes/guru/scss/base/_media.scss
- /Users/tho/htdocs/drupal_guru_testing/vdd/data/drupal8/themes/guru/scss/base/_typography.scss
- /Users/tho/htdocs/drupal_guru_testing/vdd/data/drupal8/themes/guru/scss/components/__styleguide_section.scss
- /Users/tho/htdocs/drupal_guru_testing/vdd/data/drupal8/themes/guru/scss/components/_logo.scss
- /Users/tho/htdocs/drupal_guru_testing/vdd/data/drupal8/themes/guru/scss/components/guru/_guru-browser-indicator.scss
- /Users/tho/htdocs/drupal_guru_testing/vdd/data/drupal8/themes/guru/scss/components/header/__styleguide_section.scss
- /Users/tho/htdocs/drupal_guru_testing/vdd/data/drupal8/themes/guru/scss/components/header/_logo.scss
- /Users/tho/htdocs/drupal_guru_testing/vdd/data/drupal8/themes/guru/scss/components/header/_page-header.scss
- /Users/tho/htdocs/drupal_guru_testing/vdd/data/drupal8/themes/guru/scss/components/header/_region-primary-menu.scss
- /Users/tho/htdocs/drupal_guru_testing/vdd/data/drupal8/themes/guru/scss/components/viewmode/viewmode/__styleguide_section.scss
- /Users/tho/htdocs/drupal_guru_testing/vdd/data/drupal8/themes/guru/scss/components/viewmode/viewmode/_node.scss
- /Users/tho/htdocs/drupal_guru_testing/vdd/data/drupal8/themes/guru/scss/layouts/__styleguide_section.scss
- /Users/tho/htdocs/drupal_guru_testing/vdd/data/drupal8/themes/guru/scss/layouts/_page-layout.scss
- /Users/tho/htdocs/drupal_guru_testing/vdd/data/drupal8/themes/guru/scss/main.scss
- /Users/tho/htdocs/drupal_guru_testing/vdd/data/drupal8/themes/guru/scss/module/__styleguide_section.scss
- /Users/tho/htdocs/drupal_guru_testing/vdd/data/drupal8/themes/guru/scss/variables/__styleguide_section.scss
- /Users/tho/htdocs/drupal_guru_testing/vdd/data/drupal8/themes/guru/scss/variables/_breakpoints.scss
- /Users/tho/htdocs/drupal_guru_testing/vdd/data/drupal8/themes/guru/scss/variables/_colors.scss
- /Users/tho/htdocs/drupal_guru_testing/vdd/data/drupal8/themes/guru/scss/variables/_fonts.scss
...Determining section markup:
- 4.1: inline markup
- Base - Form Elements: inline markup
- Base - Media: inline markup
- Base - Typography: inline markup
- Components - Header - Page Header: inline markup
- Components - Header - Region primary menu: inline markup
- Components - Header - Site logo: inline markup
- Components - Viewmode - Teaser: inline markup
- Variables - Color pallete - Backgrounds: inline markup
- Variables - Color pallete - Colors: inline markup
- Variables - Fonts: inline markup
...Building style guide pages:
- homepage
TypeError: rootSection.header is not a function
```

Run the reported node_modules/kss/bin/kss command with the SCSS source, styleguide destination, and styleguide-template/guru-handlebars builder. Start at the homepage-building step and inspect the builder template and the rootSection value associated with the rootSection.header error. Done means the command completes and generates the style guide.

Written by the indexing model from the issue text.