feat(series): add custom placeholders in intro

Custom placeholders are user-defined and can be used in both headline and description.

content/blog/series/01-series-introduction/index.md

@@ -8,7 +8,7 @@ tags = ["showcase", "tutorial"]
 
 [extra]
 series_page_introduction = "link"
-series_page_introduction_variables = { position = "first", toto = "TOTO!!! "}
+series_page_introduction_variables = { position = "first", foo = "FOO!!!"}
 
 +++
 

content/blog/series/02-series-pages-organization/index.md

@@ -8,6 +8,7 @@ tags = ["showcase", "tutorial"]
 
 [extra]
 series_page_introduction = "summary"
+series_page_introduction_variables = { position = "second", foo = "FOO FOO!!!"}
 
 +++
 

content/blog/series/03-series-cheat-sheet/index.md

@@ -8,6 +8,7 @@ tags = ["showcase", "tutorial", "FAQ"]
 
 [extra]
 series_page_introduction = "custom"
+series_page_introduction_variables = { position = "third", foo = "FOO FOO FOO!!!"}
 
 +++
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content/blog/series/_index.md

@@ -14,6 +14,13 @@ post_listing_index_reversed = false
 
 series_page_introduction = "none"
 
+series_page_introduction_placeholders = ["$POSITION", "$FOO", "$BAR"]
+series_page_headline = "This article is the $POSITION of the series '$SERIES_HTML_LINK' ($FOO)"
+series_page_description = """
+<p>You can put whatever you want in a custom description.</p>
+<p>All variable are accessibles, including custom ones.</p>
+<hr>
+"""
 +++
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 Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.