get hrefType() {
    const to = this.to;
    if (to.isInline && to !== this.from) {
      return 'inline';
    }
    if (!this._hrefType) {
      const href = (this.href || '').trim();
      if (/^\/\//.test(href)) {
        this._hrefType = 'protocolRelative';
      } else if (/^\//.test(href)) {
        this._hrefType = 'rootRelative';
      } else if (/^[a-z+]+:/i.test(href)) {
        this._hrefType = 'absolute';
      } else {
        this._hrefType = 'relative';
      }
    }
    return this._hrefType;
  }
Either `'absolute'`, `'rootRelative'`, `'protocolRelative'`, `'relative'`, or `'inline'`.
Decides what "degree" of relative url [`refreshHref()`]{@link Relation#refreshHref} tries to issue, except for
`'inline'` which means that the target asset is contained in a `data:` url or similar.

@type {String}