diff --git a/doc/fcconfig.fncs b/doc/fcconfig.fncs
index de7a5d7..5f1ef43 100644
--- a/doc/fcconfig.fncs
+++ b/doc/fcconfig.fncs
@@ -393,7 +393,9 @@ parse error, semantic error or allocation failure. Otherwise returns FcTrue.
 @TYPE1@		const FcConfig *		@ARG1@		config
 @PURPOSE@	Obtain the system root directory
 @DESC@
-Obtrains the system root directory in 'config' if available.
+Obtains the system root directory in 'config' if available. All files
+(including file properties in patterns) obtained from this 'config' are
+relative to this system root directory.
 @SINCE@		2.10.92
 @@
 
@@ -403,10 +405,13 @@ Obtrains the system root directory in 'config' if available.
 @TYPE2@		const FcChar8 *			@ARG2@		sysroot
 @PURPOSE@	Set the system root directory
 @DESC@
-Set 'sysroot' as the system root directory. fontconfig prepend 'sysroot'
-to the cache directories in order to allow people to generate caches at
-the build time. Note that this causes changing current config. i.e.
-this function calls FcConfigSetCurrent() internally.
+Set 'sysroot' as the system root directory. All file paths used or created with
+this 'config' (including file properties in patterns) will be considered or
+made relative to this 'sysroot'. This allows a host to generate caches for
+targets at build time. This also allows a cache to be re-targeted to a
+different base directory if 'FcConfigGetSysRoot' is used to resolve file paths.
+When setting this on the current config this causes changing current config
+(calls FcConfigSetCurrent()).
 @SINCE@		2.10.92
 @@
 
diff --git a/doc/fontconfig-devel.sgml b/doc/fontconfig-devel.sgml
index 6a6caef..b8b232c 100644
--- a/doc/fontconfig-devel.sgml
+++ b/doc/fontconfig-devel.sgml
@@ -168,6 +168,7 @@ convenience for the application's rendering mechanism.
                                                   normal hinter
     globaladvance  FC_GLOBAL_ADVANCE      Bool    Use font global advance data (deprecated)
     file           FC_FILE                String  The filename holding the font
+                                                  relative to the config's sysroot
     index          FC_INDEX               Int     The index of the font within
                                                   the file
     ftface         FC_FT_FACE             FT_Face Use the specified FreeType