#include <bits/stdc++.h>
using namespace std;
const long long INF = 1e18;


int n, m;
vector<string> sheet;
vector<vector<int>> val;
vector<set<int>> unmatch_idxs;



void flip(const string& path) {
    int i = 0, j = 0;
    for (int idx = 0; idx < path.size(); idx++) {
        if (val[i][j]) unmatch_idxs[i].erase(j);
        else unmatch_idxs[i].insert(j);
        val[i][j] ^= 1;
        if (path[idx] == 'R') j++;
        else i++;
    }
    assert(i == n-1);
    assert(j == m-1);
    if (val[i][j]) unmatch_idxs[i].erase(j);
    else unmatch_idxs[i].insert(j);
    val[i][j] ^= 1;

    // for (int i = 0; i < n; i++) {
    //     for (int j = 0; j < m; j++) {
    //         cout << val[i][j] << " \n"[j==m-1];
    //     }
    // }
    // cout << "---------------\n";
}

bool check(char goal) {
    val.assign(n, vector<int>(m, 0));
    unmatch_idxs.assign(n, set<int>());
    vector<int> check_diag(n+m-1, 0);
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            val[i][j] = (sheet[i][j] == goal ? 0 : 1);
            if (val[i][j]) unmatch_idxs[i].insert(j);
            check_diag[i+j] ^= val[i][j];
        }
    }
    // check feasibility
    for (int i = 0; i < n+m-1; i++) {
        if (check_diag[i] != check_diag[0]) return false;
    }
    // greedy
    vector<string> ans;
    // for (int i = 0; i < n; i++) {
    //     for (int j = 0; j < m; j++) {
    //         cout << val[i][j] << " \n"[j==m-1];
    //     }
    // }
    // cout << "---------------\n";
    while (true) {
        // check if done
        bool ok = true;
        for (int i = 0; i < n - 1; i++) {
            auto itr = unmatch_idxs[i].upper_bound(m-1);
            int idx = -1;
            if (!unmatch_idxs[i].empty()) {
                idx = *(--itr);
            }
            if (idx <= 0) continue;
            ok = false;
            break;
        }
        if (ok) break;
        // construct paths
        int i = 0, j = 0;
        string path = "";
        while (i < n - 1) {
            // find farthest unmatch
            auto jmp_j_itr = unmatch_idxs[i].upper_bound(m-1);
            int jmp_j = -1;
            if (!unmatch_idxs[i].empty()) {
                jmp_j = *(--jmp_j_itr);
            }
            // cout << i << " " << j << " " << jmp_j << "\n";
            // check if jump to right
            if (jmp_j > j) {
                path += string(jmp_j-j, 'R');
                j = jmp_j;
            }
            // advance to next row
            path += 'D';
            i++;
        }
        if (j != m-1) path += string(m-1-j, 'R');
        // update
        flip(path);
        ans.push_back(path);
    }
    // check if starting point is not correct
    if (unmatch_idxs[0].find(0) != unmatch_idxs[0].end()) {
        string path = string(n-1, 'D') + string(m-1, 'R');
        ans.push_back(path);
        flip(path);
    }

    cout << "YES\n";
    cout << ans.size() << "\n";
    for (auto s : ans) {
        cout << s << "\n";
    }
    return true;
}

void solve() {
    cin >> n >> m;
    sheet.assign(n, "");
    for (int i = 0; i < n; i++) cin >> sheet[i];
    if (check('B')) return;
    if (check('W')) return;
    // infeasible
    cout << "NO\n";
}



int main() {
    ios::sync_with_stdio(false);
    int T=1;
    cin >> T;
    while (T--) {
        solve();
        // cout << "===========\n";
    }
    return 0;
}