diff --git a/lm-c99/ig-c99.ysl2 b/lm-c99/ig-c99.ysl2
new file mode 100644
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+++ b/lm-c99/ig-c99.ysl2
@@ -0,0 +1,202 @@
+// p≡p API header generator
+
+// Copyleft (c) 2019-2020, p≡p foundation
+// this file is under GNU General Public License 3.0
+// see LICENSE.txt
+// written by Volker Birk
+
+
+include yslt.yml2
+
+tstylesheet {
+    include to_c.ysl2
+    include standardlib.ysl2
+
+    template "/package", "text" {
+        apply "api", 0
+    }
+
+
+    template "api" document "{@name}_api.h", "text" {
+        const "pkg_name", "../@name";
+        const "pkg_version", "../version/text()";
+        const "pkg_license", "../license/text()";
+        const "pkg_copyleft", "../copyleft/text()";
+        const "api_name", "@name";
+        ||
+        // «yml:ucase($pkg_name)» «$pkg_version»
+        // «$api_name»_api.h
+        // «$pkg_license»
+        // «$pkg_copyleft»
+        #pragma once
+
+        #ifdef __cplusplus
+        extern "C" {
+        #endif
+
+        #include <stddef.h>
+        //#include "idl.h"
+
+        // Types
+        // -----
+        ``apply "type", 0
+
+        // Enums
+        // -----
+        ``apply "enum", 0
+
+        // Structs
+        // -------
+        ``apply "struct", 0
+
+
+        #ifdef __cplusplus
+        } // extern "C"
+        #endif
+        ||
+    }
+
+
+    // TYPE
+    // ----
+
+    def "func:typedef" {
+        param "is_type";
+        param "alias_name";
+        result > typedef «$is_type» «$alias_name»;\n
+    }
+
+    def "func:idl_basetype" {
+        param "idl_name";
+        choose {
+            when "$idl_name = 'string'"
+                result > «func:typedef('char*', $idl_name)»
+            when "$idl_name = 'binary'"
+                result > «func:typedef('char*', $idl_name)»
+            when "$idl_name = 'uint'"
+                result > «func:typedef('unsigned int', $idl_name)»
+            when "$idl_name = 'size'"
+                result > «func:typedef('size_t', $idl_name)»
+            when "$idl_name = 'opaque'"
+                result > «func:typedef('void*', $idl_name)»
+        }
+    }
+
+
+    template "type" {
+        const "alias_name", "@name";
+        const "is_type", "is/@type";
+
+        if 'string-length($is_type) > 0' {
+            > «func:typedef($is_type, $alias_name)»
+        } else {
+            > «func:idl_basetype($alias_name)»
+        }
+
+    }
+
+
+
+    // ENUM
+    // ----
+
+    def "func:c_name_enum" {
+        param "pkg_name";
+        param "name";
+
+        result "yml:ucase(concat($pkg_name, '_', $name))"
+    }
+
+
+    template "enum" {
+        const "idl_name", "@name";
+        const "pkg_name", "../../@name";
+        const "enum_name", "func:c_name_enum($pkg_name, $idl_name)";
+        ||
+        typedef enum _«$enum_name» {
+            ``apply "item" with "enum_name", "$enum_name"
+        } «$enum_name»;
+
+        ||
+    }
+
+    template "item" {
+        param "enum_name";
+        const "item_name_idl", "@name";
+        const "item_name", "yml:ucase(concat($enum_name, '_', $item_name_idl))";
+
+        apply "@doc", 0, mode="multiline";
+        choose {
+            when "@output='hex'"
+                | «$item_name»`if "text()" { " = 0x" value "yml:dec2hex(., 2)" }``if "position()!=last()" > ,``apply "@doc" , 0, mode="oneline"`
+            otherwise
+                | «$item_name»`if "text()" { " = " value "." }``if "position()!=last()" > ,``apply "@doc" , 0, mode="oneline"`
+        }
+    }
+
+
+
+    // STRUCT
+    // ------
+
+    def "func:c_name_struct" {
+        param "pkg_name";
+        param "idl_name";
+
+        result "concat(yml:capit($pkg_name), '_', yml:capit($idl_name))"
+    }
+
+    template "struct" {
+        const "idl_name", "@name";
+        const "pkg_name", "../../@name";
+        const "c_name_struct", "func:c_name_struct($pkg_name, $idl_name)";
+        ||
+        typedef struct _«$c_name_struct» {
+            ``apply "field"
+        } «$c_name_struct»;
+        ||
+    }
+
+    template "field" {
+        const "field_name", "@name";
+        const "field_type", "@type";
+        ||
+        ``apply "@doc", 0, mode="multiline"
+        «$field_type» «$field_name»;`apply "@doc" , 0, mode="oneline"`
+        ||
+    }
+
+
+    // DOC
+    // ---
+
+    template "doc|@doc", mode="oneline" {
+        const "docstring", ".";
+        const "doc_lines_count", "count(str:split($docstring, '\n'))";
+        if "$doc_lines_count = 1" {
+            const "doc_line", "normalize-space($docstring)";
+            if "string-length($doc_line) > 0" {
+               >  // «$doc_line»
+            }
+        }
+    }
+
+    template "doc|@doc", mode="multiline" {
+        const "docstring", ".";
+        const "doc_lines_count", "count(str:split($docstring, '\n'))";
+
+        if "$doc_lines_count > 1" {
+            if "string-length($docstring) > 0" {
+                |
+                for "str:split($docstring, '\n')" {
+                    const "doc_line", "normalize-space(.)";
+                    if "string-length($doc_line) > 0" {
+                       | // «$doc_line»
+                    }
+                }
+            }
+        }
+    }
+
+}
+