Transforms freeplane mm to markdown md. Nodes become headings and subheadings, Notes become paragraphs. Details are not handled. Tested with Pandoc-flavored markdown. May not work: 1. Title blocks 2. Formatting which requires a specific number of spaces

mm2markdown.xsl

<?xml version="1.0" encoding="UTF-8" ?>

<!--
	
MINDMAPEXPORTFILTER md;markdown Markdown

v. 0.1
		
This code released under the GPL. : (http://www.gnu.org/copyleft/gpl.html) 
Document : mm2markdown.xsl 
Created	on : 20 November, 2013 
Author : Lee Hachadoorian Lee.Hachadoorian@gmail.com
Description: Transforms freeplane mm to markdown md. Nodes become headings
and subheadings, Notes become paragraphs. Details are not handled. Tested
with Pandoc-flavored markdown.

May not work:
* Title blocks
* Formatting which requires a specific number of spaces

Please test and suggest improvements to author, or feel free to customize
while crediting previous authors.

******************************************************************************
Based on mm2text.xsl, original notice appears below
******************************************************************************
Document : mm2text.xsl 
Created	on : 01 February 2004, 17:17 
Author : joerg feuerhake joerg.feuerhake@free-penguin.org 
Description: transforms freeplane mm
format to html, handles crossrefs and adds numbering. feel free to
customize it while leaving the ancient authors mentioned. thank you
ChangeLog: See: http://freeplane.sourceforge.net/
-->

<xsl:stylesheet version="1.0"
	xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
	<xsl:output method="text" indent="no"/>
	<xsl:strip-space elements="map node" />
	<xsl:key name="refid" match="node" use="@ID" />

	<xsl:template name="numberSign">
		<xsl:param name="howMany">1</xsl:param>
		<xsl:if test="$howMany &gt; 0">
			<!-- Add 1 number signs (#) to result tree. -->
			<xsl:text>#</xsl:text>
			<!-- Print remaining ($howMany - 1) number signs. -->
			<xsl:call-template name="numberSign">
				<xsl:with-param name="howMany" select="$howMany - 1"/>
			</xsl:call-template>
		</xsl:if>
	</xsl:template>

	<xsl:template match="/">
		<xsl:apply-templates />
	</xsl:template>

	<xsl:template match="/map">
		<xsl:apply-templates select="node"/>
	</xsl:template>
	
	<xsl:template match="richcontent">
		<xsl:if test="@TYPE='DETAILS'">
			<xsl:text>&#xA;DETAILS: </xsl:text>
		</xsl:if>
		<xsl:if test="@TYPE='NOTE'">
			<xsl:text>&#xA;</xsl:text>
		</xsl:if>
		<xsl:apply-templates/>
		<xsl:text>&#xA;</xsl:text>
	</xsl:template>

	<xsl:template match="child::text()">
		<xsl:value-of select="translate(normalize-space(.),'&#160;',' ')" />
	</xsl:template>

	<xsl:template match="p|br|tr|div|li|pre">
		<xsl:if test="preceding-sibling::*">
			<xsl:text>&#xA;</xsl:text>
		</xsl:if>
		<xsl:apply-templates/>
	</xsl:template>

	<xsl:template match="i|em">
		<xsl:text> *</xsl:text>
		<xsl:apply-templates/>
		<xsl:text>* </xsl:text>		
	</xsl:template>

	<xsl:template match="b|strong">
		<xsl:text> **</xsl:text>
		<xsl:apply-templates/>
		<xsl:text>** </xsl:text>		
	</xsl:template>

	<xsl:template match="node">
		<xsl:variable name="thisid" select="@ID" />
		<xsl:variable name="target" select="arrowlink/@DESTINATION" />
		<xsl:choose>
			<xsl:when test="count(ancestor::*) = 1">
				<xsl:text>%</xsl:text>
			</xsl:when>
			<xsl:otherwise>
				<xsl:text>&#xA;</xsl:text>
				<xsl:call-template name="numberSign">
					<xsl:with-param name="howMany" select="count(ancestor::*) - 1"/>
				</xsl:call-template>
			</xsl:otherwise>
		</xsl:choose>
		<xsl:text> </xsl:text>
		<xsl:if test="@TEXT">
			<xsl:value-of select="normalize-space(@TEXT)" />
			<xsl:text>&#xA;</xsl:text>
    		</xsl:if>
		<xsl:apply-templates select="richcontent[@TYPE='NODE']"/>
		<xsl:apply-templates select="richcontent[@TYPE='DETAILS']"/>
		<xsl:apply-templates select="richcontent[@TYPE='NOTE']"/>
		<xsl:if test="arrowlink/@DESTINATION != ''">
			<xsl:text> (see:</xsl:text>
			<xsl:for-each select="key('refid', $target)">
				<xsl:value-of select="@TEXT" />
			</xsl:for-each>
			<xsl:text>)</xsl:text>
		</xsl:if>
		<xsl:apply-templates select="node"/>
	</xsl:template>

</xsl:stylesheet> 

I haven't used YAML metadata myself. According to your link at [1], YAML blocks can appear anywhere in the document, so it might be easiest to just put them in the Note associated with the root node. Title blocks have to appear at the beginning of the document, and it appears that there can't even be a blank line above them, so it seems best to include them in the core of the root node (that and an empty root node looks weird). normalize-space() is destroying the newlines that I try to include to get the title block to look like:

% Title
% Author 1; Author 2
% Date

I have to figure out how to parse the root node and only the root node so as to not normalize spaces. (Maybe I should try turning it off for the whole document?)

I also never use node Details, and am not sure how I would use it in the kind of articles and long documents I am using mm2markdown for.

I'll have to take a look at [2] and see if I can adapt the internal link logic already included in mm2text to output Pandoc-friendly internal links.