diff --git a/src/ly_common.c b/src/ly_common.c
new file mode 100644
index 0000000..e80ca93
--- /dev/null
+++ b/src/ly_common.c
@@ -0,0 +1,925 @@
+/**
+ * @file ly_common.c
+ * @author Michal Vasko <mvasko@cesnet.cz>
+ * @brief common internal definitions for libyang
+ *
+ * Copyright (c) 2018 - 2024 CESNET, z.s.p.o.
+ *
+ * This source code is licensed under BSD 3-Clause License (the "License").
+ * You may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://opensource.org/licenses/BSD-3-Clause
+ */
+
+#define _GNU_SOURCE
+
+#include "ly_common.h"
+
+#include <assert.h>
+#include <ctype.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <inttypes.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#ifndef _WIN32
+# ifdef HAVE_MMAP
+#  include <sys/mman.h>
+# endif
+#else
+# include <io.h>
+#endif
+#include <sys/stat.h>
+#include <unistd.h>
+
+#include "compat.h"
+#include "tree_schema_internal.h"
+#include "xml.h"
+
+void *
+ly_realloc(void *ptr, size_t size)
+{
+    void *new_mem;
+
+    new_mem = realloc(ptr, size);
+    if (!new_mem) {
+        free(ptr);
+    }
+
+    return new_mem;
+}
+
+char *
+ly_strnchr(const char *s, int c, size_t len)
+{
+    for ( ; len && (*s != (char)c); ++s, --len) {}
+    return len ? (char *)s : NULL;
+}
+
+int
+ly_strncmp(const char *refstr, const char *str, size_t str_len)
+{
+    int rc = strncmp(refstr, str, str_len);
+
+    if (!rc && (refstr[str_len] == '\0')) {
+        return 0;
+    } else {
+        return rc ? rc : 1;
+    }
+}
+
+LY_ERR
+ly_strntou8(const char *nptr, size_t len, uint8_t *ret)
+{
+    uint8_t num = 0, dig, dec_pow;
+
+    if (len > 3) {
+        /* overflow for sure */
+        return LY_EDENIED;
+    }
+
+    dec_pow = 1;
+    for ( ; len && isdigit(nptr[len - 1]); --len) {
+        dig = nptr[len - 1] - 48;
+
+        if (LY_OVERFLOW_MUL(UINT8_MAX, dig, dec_pow)) {
+            return LY_EDENIED;
+        }
+        dig *= dec_pow;
+
+        if (LY_OVERFLOW_ADD(UINT8_MAX, num, dig)) {
+            return LY_EDENIED;
+        }
+        num += dig;
+
+        dec_pow *= 10;
+    }
+
+    if (len) {
+        return LY_EVALID;
+    }
+    *ret = num;
+    return LY_SUCCESS;
+}
+
+LY_ERR
+ly_value_prefix_next(const char *str_begin, const char *str_end, uint32_t *len, ly_bool *is_prefix, const char **str_next)
+{
+    const char *stop, *prefix;
+    size_t bytes_read;
+    uint32_t c;
+    ly_bool prefix_found;
+    LY_ERR ret = LY_SUCCESS;
+
+    assert(len && is_prefix && str_next);
+
+#define IS_AT_END(PTR, STR_END) (STR_END ? PTR == STR_END : !(*PTR))
+
+    *str_next = NULL;
+    *is_prefix = 0;
+    *len = 0;
+
+    if (!str_begin || !(*str_begin) || (str_begin == str_end)) {
+        return ret;
+    }
+
+    stop = str_begin;
+    prefix = NULL;
+    prefix_found = 0;
+
+    do {
+        /* look for the beginning of the YANG value */
+        do {
+            LY_CHECK_RET(ly_getutf8(&stop, &c, &bytes_read));
+        } while (!is_xmlqnamestartchar(c) && !IS_AT_END(stop, str_end));
+
+        if (IS_AT_END(stop, str_end)) {
+            break;
+        }
+
+        /* maybe the prefix was found */
+        prefix = stop - bytes_read;
+
+        /* look for the the end of the prefix */
+        do {
+            LY_CHECK_RET(ly_getutf8(&stop, &c, &bytes_read));
+        } while (is_xmlqnamechar(c) && !IS_AT_END(stop, str_end));
+
+        prefix_found = c == ':' ? 1 : 0;
+
+        /* if it wasn't the prefix, keep looking */
+    } while (!IS_AT_END(stop, str_end) && !prefix_found);
+
+    if ((str_begin == prefix) && prefix_found) {
+        /* prefix found at the beginning of the input string */
+        *is_prefix = 1;
+        *str_next = IS_AT_END(stop, str_end) ? NULL : stop;
+        *len = (stop - bytes_read) - str_begin;
+    } else if ((str_begin != prefix) && (prefix_found)) {
+        /* there is a some string before prefix */
+        *str_next = prefix;
+        *len = prefix - str_begin;
+    } else {
+        /* no prefix found */
+        *len = stop - str_begin;
+    }
+
+#undef IS_AT_END
+
+    return ret;
+}
+
+LY_ERR
+ly_getutf8(const char **input, uint32_t *utf8_char, size_t *bytes_read)
+{
+    uint32_t c, aux;
+    size_t len;
+
+    c = (*input)[0];
+
+    if (!(c & 0x80)) {
+        /* one byte character */
+        len = 1;
+
+        if ((c < 0x20) && (c != 0x9) && (c != 0xa) && (c != 0xd)) {
+            goto error;
+        }
+    } else if ((c & 0xe0) == 0xc0) {
+        /* two bytes character */
+        len = 2;
+
+        aux = (*input)[1];
+        if ((aux & 0xc0) != 0x80) {
+            goto error;
+        }
+        c = ((c & 0x1f) << 6) | (aux & 0x3f);
+
+        if (c < 0x80) {
+            goto error;
+        }
+    } else if ((c & 0xf0) == 0xe0) {
+        /* three bytes character */
+        len = 3;
+
+        c &= 0x0f;
+        for (uint64_t i = 1; i <= 2; i++) {
+            aux = (*input)[i];
+            if ((aux & 0xc0) != 0x80) {
+                goto error;
+            }
+
+            c = (c << 6) | (aux & 0x3f);
+        }
+
+        if ((c < 0x800) || ((c > 0xd7ff) && (c < 0xe000)) || (c > 0xfffd)) {
+            goto error;
+        }
+    } else if ((c & 0xf8) == 0xf0) {
+        /* four bytes character */
+        len = 4;
+
+        c &= 0x07;
+        for (uint64_t i = 1; i <= 3; i++) {
+            aux = (*input)[i];
+            if ((aux & 0xc0) != 0x80) {
+                goto error;
+            }
+
+            c = (c << 6) | (aux & 0x3f);
+        }
+
+        if ((c < 0x1000) || (c > 0x10ffff)) {
+            goto error;
+        }
+    } else {
+        goto error;
+    }
+
+    (*utf8_char) = c;
+    (*input) += len;
+    if (bytes_read) {
+        (*bytes_read) = len;
+    }
+    return LY_SUCCESS;
+
+error:
+    if (bytes_read) {
+        (*bytes_read) = 0;
+    }
+    return LY_EINVAL;
+}
+
+/**
+ * @brief Check whether an UTF-8 string is equal to a hex string after a bitwise and.
+ *
+ * (input & 0x[arg1][arg3][arg5]...) == 0x[arg2][arg4][arg6]...
+ *
+ * @param[in] input UTF-8 string.
+ * @param[in] bytes Number of bytes to compare.
+ * @param[in] ... 2x @p bytes number of bytes to perform bitwise and and equality operations.
+ * @return Result of the operation.
+ */
+static int
+ly_utf8_and_equal(const char *input, uint8_t bytes, ...)
+{
+    va_list ap;
+    int i, and, byte;
+
+    va_start(ap, bytes);
+    for (i = 0; i < bytes; ++i) {
+        and = va_arg(ap, int);
+        byte = va_arg(ap, int);
+
+        /* compare each byte */
+        if (((uint8_t)input[i] & and) != (uint8_t)byte) {
+            return 0;
+        }
+    }
+    va_end(ap);
+
+    return 1;
+}
+
+/**
+ * @brief Check whether an UTF-8 string is smaller than a hex string.
+ *
+ * input < 0x[arg1][arg2]...
+ *
+ * @param[in] input UTF-8 string.
+ * @param[in] bytes Number of bytes to compare.
+ * @param[in] ... @p bytes number of bytes to compare with.
+ * @return Result of the operation.
+ */
+static int
+ly_utf8_less(const char *input, uint8_t bytes, ...)
+{
+    va_list ap;
+    int i, byte;
+
+    va_start(ap, bytes);
+    for (i = 0; i < bytes; ++i) {
+        byte = va_arg(ap, int);
+
+        /* compare until bytes differ */
+        if ((uint8_t)input[i] > (uint8_t)byte) {
+            return 0;
+        } else if ((uint8_t)input[i] < (uint8_t)byte) {
+            return 1;
+        }
+    }
+    va_end(ap);
+
+    /* equals */
+    return 0;
+}
+
+/**
+ * @brief Check whether an UTF-8 string is greater than a hex string.
+ *
+ * input > 0x[arg1][arg2]...
+ *
+ * @param[in] input UTF-8 string.
+ * @param[in] bytes Number of bytes to compare.
+ * @param[in] ... @p bytes number of bytes to compare with.
+ * @return Result of the operation.
+ */
+static int
+ly_utf8_greater(const char *input, uint8_t bytes, ...)
+{
+    va_list ap;
+    int i, byte;
+
+    va_start(ap, bytes);
+    for (i = 0; i < bytes; ++i) {
+        byte = va_arg(ap, int);
+
+        /* compare until bytes differ */
+        if ((uint8_t)input[i] > (uint8_t)byte) {
+            return 1;
+        } else if ((uint8_t)input[i] < (uint8_t)byte) {
+            return 0;
+        }
+    }
+    va_end(ap);
+
+    /* equals */
+    return 0;
+}
+
+LY_ERR
+ly_checkutf8(const char *input, size_t in_len, size_t *utf8_len)
+{
+    size_t len;
+
+    if (!(input[0] & 0x80)) {
+        /* one byte character */
+        len = 1;
+
+        if (ly_utf8_less(input, 1, 0x20) && (input[0] != 0x9) && (input[0] != 0xa) && (input[0] != 0xd)) {
+            /* invalid control characters */
+            return LY_EINVAL;
+        }
+    } else if (((input[0] & 0xe0) == 0xc0) && (in_len > 1)) {
+        /* two bytes character */
+        len = 2;
+
+        /* (input < 0xC280) || (input > 0xDFBF) || ((input & 0xE0C0) != 0xC080) */
+        if (ly_utf8_less(input, 2, 0xC2, 0x80) || ly_utf8_greater(input, 2, 0xDF, 0xBF) ||
+                !ly_utf8_and_equal(input, 2, 0xE0, 0xC0, 0xC0, 0x80)) {
+            return LY_EINVAL;
+        }
+    } else if (((input[0] & 0xf0) == 0xe0) && (in_len > 2)) {
+        /* three bytes character */
+        len = 3;
+
+        /* (input >= 0xEDA080) && (input <= 0xEDBFBF) */
+        if (!ly_utf8_less(input, 3, 0xED, 0xA0, 0x80) && !ly_utf8_greater(input, 3, 0xED, 0xBF, 0xBF)) {
+            /* reject UTF-16 surrogates */
+            return LY_EINVAL;
+        }
+
+        /* (input < 0xE0A080) || (input > 0xEFBFBF) || ((input & 0xF0C0C0) != 0xE08080) */
+        if (ly_utf8_less(input, 3, 0xE0, 0xA0, 0x80) || ly_utf8_greater(input, 3, 0xEF, 0xBF, 0xBF) ||
+                !ly_utf8_and_equal(input, 3, 0xF0, 0xE0, 0xC0, 0x80, 0xC0, 0x80)) {
+            return LY_EINVAL;
+        }
+    } else if (((input[0] & 0xf8) == 0xf0) && (in_len > 3)) {
+        /* four bytes character */
+        len = 4;
+
+        /* (input < 0xF0908080) || (input > 0xF48FBFBF) || ((input & 0xF8C0C0C0) != 0xF0808080) */
+        if (ly_utf8_less(input, 4, 0xF0, 0x90, 0x80, 0x80) || ly_utf8_greater(input, 4, 0xF4, 0x8F, 0xBF, 0xBF) ||
+                !ly_utf8_and_equal(input, 4, 0xF8, 0xF0, 0xC0, 0x80, 0xC0, 0x80, 0xC0, 0x80)) {
+            return LY_EINVAL;
+        }
+    } else {
+        return LY_EINVAL;
+    }
+
+    *utf8_len = len;
+    return LY_SUCCESS;
+}
+
+LY_ERR
+ly_pututf8(char *dst, uint32_t value, size_t *bytes_written)
+{
+    if (value < 0x80) {
+        /* one byte character */
+        if ((value < 0x20) &&
+                (value != 0x09) &&
+                (value != 0x0a) &&
+                (value != 0x0d)) {
+            /* valid UTF8 but not YANG string character */
+            return LY_EINVAL;
+        }
+
+        dst[0] = value;
+        (*bytes_written) = 1;
+    } else if (value < 0x800) {
+        /* two bytes character */
+        dst[0] = 0xc0 | (value >> 6);
+        dst[1] = 0x80 | (value & 0x3f);
+        (*bytes_written) = 2;
+    } else if (value < 0xfffe) {
+        /* three bytes character */
+        if (((value & 0xf800) == 0xd800) ||
+                ((value >= 0xfdd0) && (value <= 0xfdef))) {
+            /* exclude surrogate blocks %xD800-DFFF */
+            /* exclude noncharacters %xFDD0-FDEF */
+            return LY_EINVAL;
+        }
+
+        dst[0] = 0xe0 | (value >> 12);
+        dst[1] = 0x80 | ((value >> 6) & 0x3f);
+        dst[2] = 0x80 | (value & 0x3f);
+
+        (*bytes_written) = 3;
+    } else if (value < 0x10fffe) {
+        if ((value & 0xffe) == 0xffe) {
+            /* exclude noncharacters %xFFFE-FFFF, %x1FFFE-1FFFF, %x2FFFE-2FFFF, %x3FFFE-3FFFF, %x4FFFE-4FFFF,
+             * %x5FFFE-5FFFF, %x6FFFE-6FFFF, %x7FFFE-7FFFF, %x8FFFE-8FFFF, %x9FFFE-9FFFF, %xAFFFE-AFFFF,
+             * %xBFFFE-BFFFF, %xCFFFE-CFFFF, %xDFFFE-DFFFF, %xEFFFE-EFFFF, %xFFFFE-FFFFF, %x10FFFE-10FFFF */
+            return LY_EINVAL;
+        }
+        /* four bytes character */
+        dst[0] = 0xf0 | (value >> 18);
+        dst[1] = 0x80 | ((value >> 12) & 0x3f);
+        dst[2] = 0x80 | ((value >> 6) & 0x3f);
+        dst[3] = 0x80 | (value & 0x3f);
+
+        (*bytes_written) = 4;
+    } else {
+        return LY_EINVAL;
+    }
+    return LY_SUCCESS;
+}
+
+/**
+ * @brief Static table of the UTF8 characters lengths according to their first byte.
+ */
+static const unsigned char utf8_char_length_table[] = {
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
+    4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 6, 6, 1, 1
+};
+
+size_t
+ly_utf8len(const char *str, size_t bytes)
+{
+    size_t len = 0;
+    const char *ptr = str;
+
+    while (((size_t)(ptr - str) < bytes) && *ptr) {
+        ++len;
+        ptr += utf8_char_length_table[((unsigned char)(*ptr))];
+    }
+    return len;
+}
+
+int
+LY_VCODE_INSTREXP_len(const char *str)
+{
+    int len = 0;
+
+    if (!str) {
+        return len;
+    } else if (!str[0]) {
+        return 1;
+    }
+    for (len = 1; len < LY_VCODE_INSTREXP_MAXLEN && str[len]; ++len) {}
+    return len;
+}
+
+#ifdef HAVE_MMAP
+LY_ERR
+ly_mmap(struct ly_ctx *ctx, int fd, size_t *length, void **addr)
+{
+    struct stat sb;
+    long pagesize;
+    size_t m;
+
+    assert(length);
+    assert(addr);
+    assert(fd >= 0);
+
+    if (fstat(fd, &sb) == -1) {
+        LOGERR(ctx, LY_ESYS, "Failed to stat the file descriptor (%s) for the mmap().", strerror(errno));
+        return LY_ESYS;
+    }
+    if (!S_ISREG(sb.st_mode)) {
+        LOGERR(ctx, LY_EINVAL, "File to mmap() is not a regular file.");
+        return LY_ESYS;
+    }
+    if (!sb.st_size) {
+        *addr = NULL;
+        return LY_SUCCESS;
+    }
+    pagesize = sysconf(_SC_PAGESIZE);
+
+    m = sb.st_size % pagesize;
+    if (m && (pagesize - m >= 1)) {
+        /* there will be enough space (at least 1 byte) after the file content mapping to provide zeroed NULL-termination byte */
+        *length = sb.st_size + 1;
+        *addr = mmap(NULL, *length, PROT_READ, MAP_PRIVATE, fd, 0);
+    } else {
+        /* there will not be enough bytes after the file content mapping for the additional bytes and some of them
+         * would overflow into another page that would not be zerroed and any access into it would generate SIGBUS.
+         * Therefore we have to do the following hack with double mapping. First, the required number of bytes
+         * (including the additinal bytes) is required as anonymous and thus they will be really provided (actually more
+         * because of using whole pages) and also initialized by zeros. Then, the file is mapped to the same address
+         * where the anonymous mapping starts. */
+        *length = sb.st_size + pagesize;
+        *addr = mmap(NULL, *length, PROT_READ, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+        *addr = mmap(*addr, sb.st_size, PROT_READ, MAP_PRIVATE | MAP_FIXED, fd, 0);
+    }
+    if (*addr == MAP_FAILED) {
+        LOGERR(ctx, LY_ESYS, "mmap() failed (%s).", strerror(errno));
+        return LY_ESYS;
+    }
+
+    return LY_SUCCESS;
+}
+
+LY_ERR
+ly_munmap(void *addr, size_t length)
+{
+    if (munmap(addr, length)) {
+        return LY_ESYS;
+    }
+    return LY_SUCCESS;
+}
+
+#else
+
+LY_ERR
+ly_mmap(struct ly_ctx *ctx, int fd, size_t *length, void **addr)
+{
+    struct stat sb;
+    size_t m;
+
+    assert(length);
+    assert(addr);
+    assert(fd >= 0);
+
+#if _WIN32
+    if (_setmode(fd, _O_BINARY) == -1) {
+        LOGERR(ctx, LY_ESYS, "Failed to switch the file descriptor to binary mode.", strerror(errno));
+        return LY_ESYS;
+    }
+#endif
+
+    if (fstat(fd, &sb) == -1) {
+        LOGERR(ctx, LY_ESYS, "Failed to stat the file descriptor (%s) for the mmap().", strerror(errno));
+        return LY_ESYS;
+    }
+    if (!S_ISREG(sb.st_mode)) {
+        LOGERR(ctx, LY_EINVAL, "File to mmap() is not a regular file.");
+        return LY_ESYS;
+    }
+    if (!sb.st_size) {
+        *addr = NULL;
+        return LY_SUCCESS;
+    }
+    /* On Windows, the mman-win32 mmap() emulation uses CreateFileMapping and MapViewOfFile, and these functions
+     * do not allow mapping more than "length of file" bytes for PROT_READ. Remapping existing mappings is not allowed, either.
+     * At that point the path of least resistance is just reading the file in as-is. */
+    m = sb.st_size + 1;
+    char *buf = calloc(m, 1);
+
+    if (!buf) {
+        LOGERR(ctx, LY_ESYS, "ly_mmap: malloc() failed (%s).", strerror(errno));
+    }
+    *addr = buf;
+    *length = m;
+
+    lseek(fd, 0, SEEK_SET);
+    ssize_t to_read = m - 1;
+
+    while (to_read > 0) {
+        ssize_t n = read(fd, buf, to_read);
+
+        if (n == 0) {
+            return LY_SUCCESS;
+        } else if (n < 0) {
+            if (errno == EINTR) {
+                continue; // can I get this on Windows?
+            }
+            LOGERR(ctx, LY_ESYS, "ly_mmap: read() failed (%s).", strerror(errno));
+        }
+        to_read -= n;
+        buf += n;
+    }
+    return LY_SUCCESS;
+}
+
+LY_ERR
+ly_munmap(void *addr, size_t length)
+{
+    (void)length;
+    free(addr);
+    return LY_SUCCESS;
+}
+
+#endif
+
+LY_ERR
+ly_strcat(char **dest, const char *format, ...)
+{
+    va_list fp;
+    char *addition = NULL;
+    size_t len;
+
+    va_start(fp, format);
+    len = vasprintf(&addition, format, fp);
+    len += (*dest ? strlen(*dest) : 0) + 1;
+
+    if (*dest) {
+        *dest = ly_realloc(*dest, len);
+        if (!*dest) {
+            va_end(fp);
+            return LY_EMEM;
+        }
+        *dest = strcat(*dest, addition);
+        free(addition);
+    } else {
+        *dest = addition;
+    }
+
+    va_end(fp);
+    return LY_SUCCESS;
+}
+
+LY_ERR
+ly_parse_int(const char *val_str, size_t val_len, int64_t min, int64_t max, int base, int64_t *ret)
+{
+    LY_ERR rc = LY_SUCCESS;
+    char *ptr, *str;
+    int64_t i;
+
+    LY_CHECK_ARG_RET(NULL, val_str, val_str[0], val_len, LY_EINVAL);
+
+    /* duplicate the value */
+    str = strndup(val_str, val_len);
+    LY_CHECK_RET(!str, LY_EMEM);
+
+    /* parse the value to avoid accessing following bytes */
+    errno = 0;
+    i = strtoll(str, &ptr, base);
+    if (errno || (ptr == str)) {
+        /* invalid string */
+        rc = LY_EVALID;
+    } else if ((i < min) || (i > max)) {
+        /* invalid number */
+        rc = LY_EDENIED;
+    } else if (*ptr) {
+        while (isspace(*ptr)) {
+            ++ptr;
+        }
+        if (*ptr) {
+            /* invalid characters after some number */
+            rc = LY_EVALID;
+        }
+    }
+
+    /* cleanup */
+    free(str);
+    if (!rc) {
+        *ret = i;
+    }
+    return rc;
+}
+
+LY_ERR
+ly_parse_uint(const char *val_str, size_t val_len, uint64_t max, int base, uint64_t *ret)
+{
+    LY_ERR rc = LY_SUCCESS;
+    char *ptr, *str;
+    uint64_t u;
+
+    LY_CHECK_ARG_RET(NULL, val_str, val_str[0], val_len, LY_EINVAL);
+
+    /* duplicate the value to avoid accessing following bytes */
+    str = strndup(val_str, val_len);
+    LY_CHECK_RET(!str, LY_EMEM);
+
+    /* parse the value */
+    errno = 0;
+    u = strtoull(str, &ptr, base);
+    if (errno || (ptr == str)) {
+        /* invalid string */
+        rc = LY_EVALID;
+    } else if ((u > max) || (u && (str[0] == '-'))) {
+        /* invalid number */
+        rc = LY_EDENIED;
+    } else if (*ptr) {
+        while (isspace(*ptr)) {
+            ++ptr;
+        }
+        if (*ptr) {
+            /* invalid characters after some number */
+            rc = LY_EVALID;
+        }
+    }
+
+    /* cleanup */
+    free(str);
+    if (!rc) {
+        *ret = u;
+    }
+    return rc;
+}
+
+/**
+ * @brief Parse an identifier.
+ *
+ * ;; An identifier MUST NOT start with (('X'|'x') ('M'|'m') ('L'|'l'))
+ * identifier          = (ALPHA / "_")
+ *                       *(ALPHA / DIGIT / "_" / "-" / ".")
+ *
+ * @param[in,out] id Identifier to parse. When returned, it points to the first character which is not part of the identifier.
+ * @return LY_ERR value: LY_SUCCESS or LY_EINVAL in case of invalid starting character.
+ */
+static LY_ERR
+lys_parse_id(const char **id)
+{
+    assert(id && *id);
+
+    if (!is_yangidentstartchar(**id)) {
+        return LY_EINVAL;
+    }
+    ++(*id);
+
+    while (is_yangidentchar(**id)) {
+        ++(*id);
+    }
+    return LY_SUCCESS;
+}
+
+LY_ERR
+ly_parse_nodeid(const char **id, const char **prefix, size_t *prefix_len, const char **name, size_t *name_len)
+{
+    assert(id && *id);
+    assert(prefix && prefix_len);
+    assert(name && name_len);
+
+    *prefix = *id;
+    *prefix_len = 0;
+    *name = NULL;
+    *name_len = 0;
+
+    LY_CHECK_RET(lys_parse_id(id));
+    if (**id == ':') {
+        /* there is prefix */
+        *prefix_len = *id - *prefix;
+        ++(*id);
+        *name = *id;
+
+        LY_CHECK_RET(lys_parse_id(id));
+        *name_len = *id - *name;
+    } else {
+        /* there is no prefix, so what we have as prefix now is actually the name */
+        *name = *prefix;
+        *name_len = *id - *name;
+        *prefix = NULL;
+    }
+
+    return LY_SUCCESS;
+}
+
+LY_ERR
+ly_parse_instance_predicate(const char **pred, size_t limit, LYD_FORMAT format,
+        const char **prefix, size_t *prefix_len, const char **id, size_t *id_len, const char **value, size_t *value_len,
+        const char **errmsg)
+{
+    LY_ERR ret = LY_EVALID;
+    const char *in = *pred;
+    size_t offset = 1;
+    uint8_t expr = 0; /* 0 - position predicate; 1 - leaf-list-predicate; 2 - key-predicate */
+    char quot;
+
+    assert(in[0] == '[');
+
+    *prefix = *id = *value = NULL;
+    *prefix_len = *id_len = *value_len = 0;
+
+    /* leading *WSP */
+    for ( ; isspace(in[offset]); offset++) {}
+
+    if (isdigit(in[offset])) {
+        /* pos: "[" *WSP positive-integer-value *WSP "]" */
+        if (in[offset] == '0') {
+            /* zero */
+            *errmsg = "The position predicate cannot be zero.";
+            goto error;
+        }
+
+        /* positive-integer-value */
+        *value = &in[offset++];
+        for ( ; isdigit(in[offset]); offset++) {}
+        *value_len = &in[offset] - *value;
+
+    } else if (in[offset] == '.') {
+        /* leaf-list-predicate: "[" *WSP "." *WSP "=" *WSP quoted-string *WSP "]" */
+        *id = &in[offset];
+        *id_len = 1;
+        offset++;
+        expr = 1;
+    } else if (in[offset] == '-') {
+        /* typically negative value */
+        *errmsg = "Invalid instance predicate format (negative position or invalid node-identifier).";
+        goto error;
+    } else {
+        /* key-predicate: "[" *WSP node-identifier *WSP "=" *WSP quoted-string *WSP "]" */
+        in = &in[offset];
+        if (ly_parse_nodeid(&in, prefix, prefix_len, id, id_len)) {
+            *errmsg = "Invalid node-identifier.";
+            goto error;
+        }
+        if ((format == LYD_XML) && !(*prefix)) {
+            /* all node names MUST be qualified with explicit namespace prefix */
+            *errmsg = "Missing prefix of a node name.";
+            goto error;
+        }
+        offset = in - *pred;
+        in = *pred;
+        expr = 2;
+    }
+
+    if (expr) {
+        /*  *WSP "=" *WSP quoted-string *WSP "]" */
+        for ( ; isspace(in[offset]); offset++) {}
+
+        if (in[offset] != '=') {
+            if (expr == 1) {
+                *errmsg = "Unexpected character instead of \'=\' in leaf-list-predicate.";
+            } else { /* 2 */
+                *errmsg = "Unexpected character instead of \'=\' in key-predicate.";
+            }
+            goto error;
+        }
+        offset++;
+        for ( ; isspace(in[offset]); offset++) {}
+
+        /* quoted-string */
+        quot = in[offset++];
+        if ((quot != '\'') && (quot != '\"')) {
+            *errmsg = "String value is not quoted.";
+            goto error;
+        }
+        *value = &in[offset];
+        for ( ; offset < limit && (in[offset] != quot || (offset && in[offset - 1] == '\\')); offset++) {}
+        if (in[offset] == quot) {
+            *value_len = &in[offset] - *value;
+            offset++;
+        } else {
+            *errmsg = "Value is not terminated quoted-string.";
+            goto error;
+        }
+    }
+
+    /* *WSP "]" */
+    for ( ; isspace(in[offset]); offset++) {}
+    if (in[offset] != ']') {
+        if (expr == 0) {
+            *errmsg = "Predicate (pos) is not terminated by \']\' character.";
+        } else if (expr == 1) {
+            *errmsg = "Predicate (leaf-list-predicate) is not terminated by \']\' character.";
+        } else { /* 2 */
+            *errmsg = "Predicate (key-predicate) is not terminated by \']\' character.";
+        }
+        goto error;
+    }
+    offset++;
+
+    if (offset <= limit) {
+        *pred = &in[offset];
+        return LY_SUCCESS;
+    }
+
+    /* we read after the limit */
+    *errmsg = "Predicate is incomplete.";
+    *prefix = *id = *value = NULL;
+    *prefix_len = *id_len = *value_len = 0;
+    offset = limit;
+    ret = LY_EINVAL;
+
+error:
+    *pred = &in[offset];
+    return ret;
+}