all: fix the logic when applying default embedded CSS

By default, the document contains ":stylesheet:" attribute, which
means using the default embedded CSS.
To disable it, unset the attribute using ":stylesheet!:".
To overwrite it, set the attribute to path of CSS file
":stylesheet: my.css".

While at it, export the DocAttrStylesheet.

1 files changed, 2 insertions, 2 deletions

diff --git a/document.go b/document.go
index aa89434..1fa88ed 100644
--- a/document.go
+++ b/document.go
@@ -215,8 +215,8 @@ func (doc *Document) ToHTML(out io.Writer) (err error) {
 
 	var ok bool
 
-	_, ok = doc.Attributes.Entry[docAttrStylesheet]
-	if ok {
+	docAttrValue, ok = doc.Attributes.Entry[DocAttrStylesheet]
+	if ok && len(docAttrValue) == 0 {
 		buf.WriteByte('\n')
 		buf.WriteString(_defaultCSS)
 	}